Jules, are you using a monopod to hold up that 300 f2.8? Great lens, especially for night football, but no lightweight. My son has the Canon version, and it weighs in at 6+ pounds. Worth it, but hard to hold at eye level for extended periods.
TriX at my age I always use a monopod for the 300, 200-500 5.6. No way could I shoot for more than 12 seconds without one. I still have trouble with the focus on the 300 2.8 going from near to far. Any suggestions? Just won't click in?