Thanks to all for the helpful replies.

My daughter plays soccer, and I take a lot of pictures of her games using a Canon 100-400 II on a 7D Mark ii. I get good results from daylight games, but when they play at night -- usually on fields with pretty bad lighting -- the pictures tend to be marginal at best. Even when I use the slowest shutter speed I can get away with, I often wind up with a too-high ISO, and I get noisy, often dark pictures. I'm thinking maybe I need a faster lens for night shots, which probably means a prime telephoto. I'd appreciate any suggestions from folks who shoot outdoor sports at night, especially youth sports where the lighting tends to be poor. Thanks in advance.