Back in the 90s, my middle school had a policy of punishing any students involved in a fight. If you threw a punch, you were in trouble. If you got hit, you were in trouble. The official line being that it would be unfair to punish two students brawling simply because the teacher didn't arrive until the last punch was thrown. But in practical terms, it meant you had a huge disincentive to report being attacked because it would amount to a confession of guilt.

Found this out very personally when a kid in a foul mood decided to start marching through the hallway and swinging at anyone standing in his way. He struck three kids on his way out of the building (including myself). When this got up to the principal's office, the principal was forced to explain to three different sets of parents why their children were in trouble because one (older, btw) child went on a rampage.

In that particular incident, the offending kid was suspended and ultimately moved to a disciplinary school. But the policy wasn't changed, just exempted in this particular instance.