I just saw someone knitting something yellow at the U.S. Open Tennis Tournament in NYC. It was during the Del Potro/Simon match. (Simon ended up winning the match.) They were panning around the stadium when I saw it.
I have found from personal experience that knitting at sporting events is not the best idea for me. I jump up and down, yelling a lot, not to mention the food and drink component that makes it so messy. Maybe knitting at tennis matches works for some people, but it bores me to tears. I would think keeping your eye on the ball, thwap thwap thwap, would make only the simplest projects possible, but that's just me.
There is a lady who goes to the tennis here in 'OZ', I think it's the Australian Open (not a bit tennis fan). Anyhow, each year the cameramen seem to find her and the presenters this year commented on how they see her knitting away every year "how can she do that and watch tennis at the same time..." they say