Btw the fact that trip is an encounter power does not necessarily mean that it will be useable once per encounter.
You could have a Recharge when you grapple someone.
You could have additional trips if you are using weapons that are designed for tripping.
You could have a feat that allows you to use trip several times per encounter.
It could well be at will for Monks.
4E fighter is a heavily armored weapon user. Unless such a character is specialised in a weapon designed for tripping, I would not see him attempt to trip someone anyway. How on earth does someone in heavy plate manage the positioning and maneuvering required by tripping with an unarmed strike anyway?
You could have a Recharge when you grapple someone.
You could have additional trips if you are using weapons that are designed for tripping.
You could have a feat that allows you to use trip several times per encounter.
It could well be at will for Monks.
4E fighter is a heavily armored weapon user. Unless such a character is specialised in a weapon designed for tripping, I would not see him attempt to trip someone anyway. How on earth does someone in heavy plate manage the positioning and maneuvering required by tripping with an unarmed strike anyway?