In case you don’t know this, following someone is not a crime and certainly does not justify the person being followed launching a physical atatck.
And you want to know what a broken nose has to do with a person’s claim they were attacked? Because a broken nose is a “common injury”?
Ive watched many a prize fight in which no one’s nose is broken, and I’ve been in fights without breaking or getting one broken.
I’d say a broken nose in a fight is not common.
I would guess you haven't seen many bar fights. Movies sort of cover up the fact that blood and teeth actually fly, when people go at it bare knuckles style.