I'm sure that two of the worst tempered matches I've been involved in were both double-headers. The first was just non-stop chipping away at my decision making, along with players leaving a boot in after a tackle - nothing awful, but every single player on the pitch seemed to be doing it by the end and even generous application of yellow cards wasn't slowing them down.
The other one is pretty much the only near 22-man mass brawl I've been involved in. Again, by the "4th half", tensions had been gradually creeping up and one late tackle crashes in. Immediately, 3 or 4 players from each team arrive to square up. And when I'd just about calmed that down, the rest of the players erupt. Apparently someone completely uninvolved in the first incident had randomly decided to spit at the nearest opponent while I was busy dealing with the first incident. And I'm not convinced that would have happened if his team hadn't already lost 3 points thanks to losing the first match.
I'll give double headers one more go if asked, but if that's as bad, I'll take a lot of persuading to take on another one.