My grammar school, Humberstone Foundation School existed in distant rivalry with Wintringham School, which was a day grammar school like itself. The schools liked to beat each other at sports matches.
One night the Humberstone Upper Sixth staged a raid, captured the other school's flagpole and erected it in a clearing in the local wood. They tipped off the other school afterwards so it could be recovered. Retaliation for this humiliating slight was a possibility, so the Upper Sixth set up a rota of night watches, reckoning that it would be enough if guard was kept until 1.0 am.
I was in the Lower Sixth, but four of us were invited to assist, so we visited the school after dark to keep watch in pairs. It was quite exciting creeping around the school grounds at night.
It didn't happen on my watch, but one night, intruders were seen pouring over the school fence just after midnight. The two on watch switched on their torches and ran toward the interlopers shouting at full voice. The startled miscreants fled in panic, abandoning pots of whitewash. The commotion attracted attention and authority was summoned.
The ringleaders at both schools were duly punished, but those lower down, including me, were not implicated and escaped punishment.