if anything you might need it when you're trying to barge players out of the way! :D

I would not look at the bicep as a muscle in isolation. It is used while swinging the arms while running. Also while running and kicking, the lwer body is creating massive forces that need to be counteracted for deceleration. Having a strong upper body and torso will help this and reduce the likiness of imbalances between the upper body and the lower body.

So yes, the bicep is important but not nearly as much as the leg and trunk. I would not work on it in isolation but part of a pulling movement such as chins, rows etc.

I agree with Alex that you should not take the bicep in isolation especially when conditioning for a sport like football. You have to think about the movement pattern in the gym and how much carry over it has to the sport? It would be better to strengthen your body as a whole through compound three dimensional movment patterns, as this will prevent injury and improve performance. Chins and Rows are good but you could also combine total body movements such as Multi directional lunges with combination curls to presses or squats with presses. Also if you are training for sports you have consider speed of movement as well as type of surface you will be playing on. As if you are playing indoors you will probably need to train righting reflexes and if you are outside you will need to train both your righting and tilting reflexes.