Considering what you are saying and considering that virtually all fights that happen are cops versus suspects, a check could be added so that citizens cannot trip/tickle cops and cops cannot trip/tickle citizens.
BTW, I say "citizens cannot trip/tickle cops" instead of "suspects cannot trip/tickle cops" as people do not do that in real life and if someone did that to a cop, there is a chance that he might cease the opportunity and kill the cop by stomp or other, thus deathmatching.
Any other circumstances such as a citizen versus citizen fight where by someone uses trip or tickle should be reported to admin. I actually thought of an idea that might help this problem:
If a player tickles or trips another player, the victim becomes "untouchable" (Do not take this as invulnerable, just read on and you'll see what I mean). The only way for the victim to have to the "untouchable" status removed is by somehow canceling the animation (mashing the keyboard or what not). During this time, if any player attacks the "untouchable" victim, that player gets frozen (proper frozen so no one can attack him/her) for about 5 seconds, gets warned and gets a pm such as "It is forbbiden to trip or tickle a player during combat."