Yeah, the basic concept of parry is when you use your sword to block someone elses.
However, I have seen it attempted by y0shi where you swing as your enemy swings.. With Tribes' netcode, this is almost impossible ot pull off.
My system isa bit different..
You must have a 1-handed weapon, and you must also have a parrying weapon.. like a rapier/main gauche combo.
It is based off the fact that it greatly increases your dodging, while you take 2-3 times as muxh damage if you get hit.. Also, you hit 2-3 times more often while in parry mode..
The more mosters you have on you at 1 time, the more of a chance you have of getting hit..
It is a bit more complicated than that, but that is the basic idea.