Naruto could initially be angry. He might think Sakura overreacted. But then, after a moment, he would probably realize his own mistake if there was one. He'd then try to play it off with a joke to ease the tension between them, like he always does in tough situations.
Well, it could be that Naruto misinterprets something Sakura says to Sasuke and makes a comment that offends her deeply. Sakura, being the strong - willed character she is, doesn't hold back and punches Naruto. This could then start a chain of events where Naruto tries to make amends, and through this process, their friendship becomes stronger as they understand each other better.
In a fanfic, if Naruto punched Sakura, it could be due to a major misunderstanding. Maybe Sakura was being controlled by an enemy's jutsu and Naruto, in his haste to stop her from doing something dangerous, resorted to physical force. This would create a huge rift in their relationship, and Sasuke might get involved to either side with Naruto or defend Sakura.
At first, Naruto would likely be extremely shocked. He has always considered Sakura a friend and teammate, so this would be a huge blow. He might question his own judgment in trusting her.
Sakura might react by being more assertive around Naruto. Instead of being shy or holding back, she could be more forward in showing her friendship or even her deeper feelings. She may also try to intimidate the fangirls in a way, like using her strength as a ninja to show that she is not one to be trifled with.
Sakura would likely be devastated. Naruto has been her friend and teammate for a long time. His death would leave a huge void in her life, and she'd probably go through a long period of mourning.
Sakura might initially be confused. She would probably wonder why Naruto is acting this way all of a sudden. For example, she might try to get his attention by calling his name a few times, but when he doesn't respond, she could be left feeling a bit bewildered.
At first, Naruto could be hesitant. He would remember the pain of the betrayal. However, as Sakura tries to make up for it, Naruto would start to warm up to her again. He might test her loyalty in small ways, like asking her to help with a difficult task. If she succeeds, he would fully accept her back into his circle of trust.
Kakashi would be more of a supportive figure. He has seen Naruto and Sakura grow up, and he would likely be happy for them. He might offer some advice to Naruto on how to handle this new relationship, especially considering the challenges they might face as ninjas. For Sakura, he could give her words of encouragement to be true to her feelings.
Sasuke might initially be a bit aloof but secretly be happy for them. He's always had a complex relationship with Naruto and Sakura, and deep down, he would see that they are good for each other.
Clint would probably be in a lot of pain, but his training would kick in. He might first try to assess the severity of his injuries. If the punch didn't daze him too much, he'd immediately start looking for a way to counter - attack those who are attacking him. Even if he's been stabbed and shot, he'd use his skills to find cover and plan his next move.