Sure, some of those altercations were provoked by the other guys, but if you're on the receiving end of such behaviour, you can always try to defuse rather than escalate. You never know who you're dealing with, if they're proficient in martial arts or carrying some kind of weapon and so on. Getting physical should be a last resort. It's not worth the potential trouble for some alpha male chest-thumping, in my opinion. Maybe it's not very alpha, but it's sensible.
With Justin, simply saying "hands off" would probably have been enough to get him to back off; with Sai, you could just try walking around him or pushing him out of the way first. If he took things further... then you'd just be defending yourself.
With Dwight, the MC leans in so close to him they almost butt heads. Okay, Dwight likes it, but the MC couldn't have known how he would react. Another guy could have responded with something like "oooh, look, boys, we've got a tough guy here" and continued this later when the coaches and girls wouldn't be around.
You don't have to be the instigator to get into unnecessary fights.
Literally nothing happened in a scene with Dwight. Maybe if it was Larry instead of Dwight we would see a kiss at least
Or maybe he would be intrigued by the MC's mighty balls and decide to carry out his signature inspection of him, right there and then? Then Dwight and Mister Stahl would join in aaand... boom! You passed! There's your spot on the first team, son.