The thing needs to be tweaked is running speed in cRPG, especially side running speed. I don't team hit much, but when one person can run faster than my swing goes, it's pretty normal I have to hit teammates from time to time with it.
Implementing another negative effect for team hits will only increase amount of annoying AGI builded chars (8-10 ATH and light armor), who seems to have fun seeing enemies hitting each other, after running around them like trained monkey. They already has huge advantage by spamming side attacks, often with light speed katanas, they don't need to be able to run around you with this kind of speed. That's the main thing which need to be looked at, no matter if you are talking about realism or game balance, this kind of running speed is just bad for everything.
You already loses points for team hits (therefore you can miss valour if you team hit too much). So why adding more penalties, if you can just fix main reason of team hits?
