I have an Idea that should help.
1. A friendly mech cannot take more than 15 points of friendly fire damage in a 3 second period. Additional damage over that amount doesn't register.
2. A friendly mech that causes 10 damage to a friendly mech in a 5 second period has its weapons locked and is unable to fire for 15 seconds.
3. Any additional lock downs increase in time period. second lock down lasts 1 minute, third would last 2 minutes ect.
Helps stop trolls. Doesn't cause extreme punishments for anyone who does it accidentally. Time and damage values could be tweaked to be lower to be harsher, and raised to be more forgiving.
would still need to report team killers but overall it would greatly stop the number of blood thirsty trial trolls.