As an avid D&D player over the last few years, I've had to give this question a lot of thought. Initially, I thought I should just go with the best spell of all time, Fireball. But it has to be non-lethal, so there goes that. My next thought was being able to cast Fly on myself. I imagine a speedy corner who could literally fly around the field would cause a massive amount of disruption to an offense. And while that would be super fun, I had one other idea that I think could be just as exciting. Cloak of Invisibility. Imagine that the quarterback drops back to pass, sees a receiver WIDE OPEN, and lets the ball fly. Then, out of nowhere, a cornerback pops into view and intercepts the ball. As the offense is trying to figure out what just happened, I'd pop the hood back up on the cloak, turn invisible, and run the other way. I'd drop the invisibility just as I crossed the goal line. Pick six. Can't beat that.