I just don't like Hailstar because of this situation with Reedfeather as it's similar to what Darktail does decades later:
And because he let Rainflower talk him into renaming Stormkit as Crookedkit. That and making Leopardpaw an apprentice early proves to me he's definitely a pushover when it comes to his own Clan's demands.
I personally don't see how it's similar though. The objectives on the matter were different. His clan were fighting to get the kits back to their mother, and Reedfeather was trying to stop them. He attacked Hailstar, and later Hailstar over powered him and almost drowned him in the process. He doesn't kill Reedfeather in the heat of the moment, but it also was to show the reader that he is capable of killing Reedfeather for the sake of his clan. They are RiverClan cats after all, and the water is their domain, they can easily drown more land-abiding cats.
Also keep in mind that WindClan only got the kits because they showed up and threatened RiverClan in the first place. They pointed out how they knew RiverClan was weak at the time, after giving up Sunningrocks and too advantage of that opportunity. Knowing that they'd have no choice but to give up the kits to Reedfeather without a fight at the the time.
Reedfeather stood up. “I’ve come to ask for what is mine.”
Willowkit and Graykit tumbled out of the nursery. Fallowtail reached after them but they escaped her paws and bounded into the clearing. “I’ve never seen a WindClan cat!” Willowkit gasped. Graykit screwed up her face. “He smells weird!”
“Hush!” Birdsong wrapped her tail around them and pulled them close as Fallowtail slid from the nursery. Cedarpelt crossed the clearing and stood beside the queen, a growl rumbling in his throat. Crookedpaw lifted his chin, proud that his mentor was so protective of his littermate and her kits.
Reedfeather dipped his head. “I’ve come to take my kits home.”
Cedarpelt stiffened. “His kits?” Crookedpaw stared. How could a WindClan cat have kits in RiverClan?
“You can’t!” Fallowtail’s cry was desperate. There was a gasp from the cats in the clearing. Crookedpaw looked from one face to the other. Slowly images stirred in his mind. Willowkit and Graykit had no father in RiverClan—or at least not one that Fallowtail had named. Crookedpaw had seen Fallowtail in WindClan territory with a tom two moons before the kits were born. Could Reedfeather be their father?
Rippleclaw turned his snarl from the WindClan warrior and glared at Fallowtail, who looked as if her world were ending. “You’re not even going to deny it? Have you forgotten the meaning of loyalty?”
Fallowtail pushed Birdsong out of the way and gathered her kits close to her belly. “I am loyal!” Fallowtail’s eyes sparked with grief. “I haven’t seen Reedfeather in moons. I love my kits more than my own life and I planned to bring them up as true RiverClan warriors.” She stared at Reedfeather. “How can you even suggest taking them away from me?”
The WindClan warrior returned her gaze. “They are as much mine as yours.” Willowkit stared up at her mother. “He can’t be our father,” she whimpered. “He doesn’t smell like us.”
Hailstar padded across the clearing and stopped beside the queen. “Is this true?” Fallowtail stared at the ground, pulling her kits closer with her tail.
Shellheart sighed. “These kits have a right to be with their father.” Crookedpaw watched, his heart twisting. Shimmerpelt crossed the clearing and pressed against Fallowtail. “You can’t make her give up her kits.” Piketooth lashed his tail. “Kits should be with their mother!”
“We can’t give them up!”
“They were born in RiverClan!”
“How can we let strangers raise them?”
A snarl cut dead the Clan’s murmuring. “How can we trust them, knowing they are half WindClan?” Rippleclaw’s eyes shone. Tanglewhisker shook his head. “He’s right,” the elder murmured. “We’ll never truly know where their loyalties lie.”
Graykit squirmed free of her mother. “We’re RiverClan!” she cried. “We’ll always be RiverClan.”
“You’re WindClan, too.”
Reedfeather spoke up. “They will be well cared for,” he promised. “We have plenty of prey.” He scanned the clearing, his gaze lingering on the dens crowding the fallen tree. “You have enough mouths to feed. What if there’s another flood? Or the river freezes? It’s happened before.” His gaze returned to the kits. “They’ll grow stronger on WindClan prey.”
“No.” Hailstar padded between Reedfeather and Fallowtail.
Reedfeather’s gaze hardened. “If it comes to war, WindClan will fight for them.”
Hailstar unsheathed his claws. “RiverClan isn’t scared by threats!”
“You should be,” Reedfeather meowed. “Don’t think the other Clans haven’t seen how you gave up Sunningrocks without a fight. RiverClan is weak. My Clanmates will join me to take back what is mine. You should fear us, old cat.” Tension spiked the air.
Then Fallowtail’s mew broke the silence. “I’ve caused enough trouble,” she whispered. “I don’t want bloodshed. Nothing is worth that.”
Crookedpaw felt sick. Don’t give up! Fight for them! He stared in disbelief as Fallowtail backed away from her kits. “Fallowtail?” Willowkit blinked at her mother. Graykit spun around. “What’s happening?”
Hailstar stared at the queen. “Are you sure?” She nodded. “Reedfeather is right. Our kits will fare better in WindClan. And we cannot risk war over my . . . my mistake.” Graykit scrambled after her mother, but Hailstar nudged the kit away with his muzzle.
“You’re going to live in your father’s Clan,” he meowed softly. Willowkit stiffened. “How can he be our father? I’ve
never seen him before!”
“He smells horrid!” Graykit flinched away as Reedfeather sniffed each kit gently.
“You’ll be well taken care of,” he told them. “WindClan is looking forward to meeting you.” Willowkit searched desperately for her mother’s gaze but Fallowtail stared at the ground.
Crookedpaw wanted to race from where his paws were rooted and beg the queen not to let them go. But, like his Clanmates, he sat in silence as Hailstar nudged the kits toward their father. “No!” Graykit yelped in terror as Reedfeather scooped her up. “Fallowtail!” He padded toward the camp entrance.
Willowkit stared wildly around the Clan. “Aren’t you going to stop him?”
“Willowkit!” Graykit struggled. “Don’t leave me!” Stumbling, Willowkit followed. “I’m coming, Graykit! I’m coming!” As they disappeared through the tunnel, Hailstar padded slowly to his den.
Birdsong pressed against Fallowtail. “They won’t forget you.” Shimmerpelt rubbed her muzzle against the queen’s cheek. “You’ll see them again. They’ll always be your kits.” Fallowtail tore away from her Clanmates and staggered toward the nursery.
Rippleclaw snorted. “What does she want to go there for?” Ottersplash spun around and hissed at the silver warrior. “Shut up! Just shut up!”
Crookedpaw darted after the grief-stricken queen and squeezed into the nursery after her. He searched for words to comfort her as she collapsed into her nest. How could anyone let a queen be separated from her kits? His heart ached for Willowkit and Graykit. They’d be terrified without their mother. He crouched down beside Fallowtail and pressed against her trembling flank. “I wouldn’t have let him take them,” he whispered. “If I was leader.”
Hailstar was very much willing to go to war and fight for the kits, but it's because of Fallowtail, and her guilt for the situation, that they didn't. She gave the kits up to avoid bloodshed, especially when their clan was already weak and suffering at the time. Where as Reedfeather is right, he does have a right to the kits because he is their father, I still think it was wrong for him to separate them from their mother and birthclan, it's quite the traumatizing situation for them. They should have at least been old enough to decide for themselves before something could have ever been suggested, but they were barely that old at the time they were taken.
Also, the fight wasn't as one-sided as some may think it was, Reedfeather at least almost killed Hailstar, or took one of his lives. Even if a cat isn't from RiverClan, some cats still have some ways to survive and swim, or float in the water by instinct. But we find out through Crookedpaw that Reedfeather can't swim at all, he makes that clear when he preferred not to cross the shallow water into RiverClan, something even an apprentice can cross, and asked to use the stepping stones which was further down, and took longer to get to.
When it comes to the fight itself-
Spitting, Reedfeather struck the RiverClan leader with a blow so fierce it sent him crashing against a rock. Crookedpaw’s breath stopped. Hailstar lay still.
Get up! Get up! Had the RiverClan leader given his final life to save the kits? Reedfeather charged for the shore, following his Clanmates. He paused at the river’s edge as the others waded in, snarling. Ottersplash and Owlfur turned in the shallows and met their pursuers with a flurry of vicious swipes. Knocking one WindClan warrior back, Owlfur spun around and sent another floundering out of his depth with a mighty blow. Ottersplash dived under the belly of a dark tabby tom and sent him lurching off balance with a heave of her shoulders.
As their Clanmates held off WindClan, Rippleclaw and Timberfur plunged toward RiverClan, necks stretched as they held the kits above water. Reedfeather stared wildly as the RiverClan warriors staggered from the river and dropped the kits on the marshy bank. His Clanmates struggled back to shore on the WindClan side and hauled themselves out.
Reedfeather turned to them in dismay. “We can’t give up! Those are my kits!” Without waiting for an answer, he whirled around and leaped into the river. “Give them back!” he screeched. Behind him, Hailstar moved. He struggled to his paws and pelted after Reedfeather. With a grunt of effort, he jumped onto the WindClan deputy’s back, sending him flailing forward into the river.
As Reedfeather surfaced, spluttering, Hailstar lunged forward with his front paws outstretched and thrust the WindClan warrior beneath the water. His eyes glowed, reflecting the rising sun, as he held Reedfeather down. The other WindClan warriors backed away up the slope, their eyes as round as owls’.
Bubbles rose around Hailstar’s paws. Reedfeather was fighting for his life. Let him go! Crookedpaw leaned forward, trembling. Don’t kill him! The kits are safe!
“Hailstar? Hailstar! Stop!” Owlfur splashed to his leader’s side. “You’re killing him.” Hailstar gazed at his Clanmates, dazed. He released his grip and staggered backward. Owlfur tugged at Reedfeather’s pelt. “Help me get him out!” he spluttered. Hailstar darted forward and grabbed Reedfeather’s scruff. Together they dragged him to the shore on WindClan’s side. Weak with relief, Crookedpaw hurried toward the kits.
Rippleclaw pressed against Willowkit while Timberfur lapped at Graykit’s dripping fur. The kits’ gaze was fixed on the far shore where Hailstar and Owlfur leaned over their father’s limp body. “Is he dead?” Willowkit wailed. Owlfur began to rub Reedfeather’s chest.
“Should I get Brambleberry?” Crookedpaw offered. Rippleclaw looked up, his eyes dark. “It’d be too late.” Suddenly Reedfeather coughed, twisting and vomiting river water.
“He’s alive!” Willowkit’s eyes shone. Then she turned and stared at Crookedpaw. “Is he going to take us home now?”
“This is your home!” Fallowtail exploded out of the reeds. She skidded to a stop and stared, huge- eyed, at her kits. “You’ve grown,” she breathed. “You’ve grown so big.” Her mew cracked.
“Fallowtail!” Graykit ducked away from Timberfur and raced to her mother, rubbing her muzzle along Fallowtail’s jaw and purring loud enough to wake the birds. Willowkit rushed to join her, tucking herself under Fallowtail’s belly.
On the far shore, the WindClan warriors were helping Reedfeather up the slope. His drenched fur clung to his bony shape, and he was limping badly. Owlfur slid into the water and swam toward home. Hailstar followed. Crookedpaw shivered. Just for a moment, Hailstar had wanted to kill Reedfeather. Not for his own sake—Reedfeather had done nothing to him personally—but for the sake of his Clan, because Hailstar truly believed the kits belonged to RiverClan.
Will I ever fight like that? A voice breathed in Crookedpaw’s ear. Mapleshade! Her mew was fierce. One day it will be your turn
to show your Clan you are worthy of being their leader, Crookedpaw. I have faith in you, young warrior.
A few things to note about the fight is that, like I pointed out before, Reedfeather either took one of Hailstar's lives, or almost took his last one, we're not sure because it's from Crooked's POV. But either way Reed did enough damage to Hailstar to mess him up in that moment.
When Hailstar got back to his paws, the only thing he was thinking about was defending his clan and protecting the kits, so he leaped onto Reedfeather and held him under the water, in an attempt to stop him.
It's noted that the look in his eyes were like a rising sun, almost like determined fury, and when Owlfur stops him, he's noted to be in a dazed, meaning unable to think properly. He was not thinking right when he did what he did, and it's most likely from when Reedfeather smashed him against the rock before. He was definitely out of it, and most likely running on battle instinct to protect the kits at that point. Doesn't make what he almost did morally right though, but also shows he's not a pushover, a berserker in battle even, but thankfully his clanmates were able to snap him out of it.
On the other hand, what Darktail did was with different intention and very consciously made decisions. He was a sadistic cat that found enjoyment in lying to others when they wanted to leave, giving them a false sense of security, before he and his gang dragged them to the lake and drowned them as punishment. He wasn't dazed, or bewildered in the head like Hailstar was, he was aware of what he was doing, and did it with the intention to kill and punish anyone he pleased. Nor did he have mercy for those cats, they were as good as dead. And if anything it was also out of convenience, since it's the easiest way to kill a cat, without them fighting back, the odds of surviving a fight against like 5 other cats holding you underwater is unlikely.
Context and intent are very important when reading into the actions of certain characters.