I think most people would appreciate it if there was a punishment for repeatedly injuring your teammates. What I suggest is that temporarily whatever item class did the damage gets disabled except for the crappiest possible item in that class. And the punishment kicks in if you team wound 3 or more times in 30 seconds. I would suggest making it last for about 10 minutes so it would be in place for most of a map. Or if it would be simpler, just make it last for the duration of the map.
So if you teambump or couch 3+ times in 30 seconds with a horse, all your good horses disappear from your equipment selection and you can only select Sumpter Horses
If the crime is done with 1H weapons, then you can only select Practice Dagger
For 2H, Practice Longsword
For polearms, the trident is the cheapest, but there might be a crappier weapon you can get
For throwers, Rocks
For archers, Short Bow and regular Arrows
And for crossbows, you should probly just not be allowed any