Shooting video of American football, best lens?

Hello everyone...

I have been tasked to shoot video of the games of a local American football club here in Denmark.
Usually it will be shot from a scaffolding tower built at the 50 yard line. I previously used a video camera, but found that I spent too much energy on keeping it in focus.

I recently put up the downpayment for the Blackmagic Cinema Camera (was going to get it for other reasons anyway), so is there a lense, I can set to infinite focus, and zoom away on? Or am I still screwed?

Regards
Peter