monopod or tripod
A monopod will allow you to get the weight off - it does pretty much all the "work." They are very easily moved from place to place or to get out of the way. Sports fields are generally pretty flat so you don't need a lot of elevation change.
If you are standing or sitting in one place and won't be in others' way, aren't in a position where you may need to move quickly for your or a player's safety, a tripod can be useful. Even a footed monopod might have some use if seated in stands or restricted in moving around - however, since the legs of tripods/footed monopods are fixed in place, they remain a danger if in an area where players might come crashing through.
Depends somewhat on the sport and your objectives. If you are trying to capture any/all of the players, a tripod may be confining. If you have a sport where you have predictable positions and you'd rather not dash about, a tripod may make it easier.