A “17” is a common conditioning exercise. It’s when a player runs from one sideline to the other, and then back 17 times.
As the player runs from one sideline to the other, that counts as 1. On return, it’ll be 2. The player is to do this until 17 is reached (always ending on the opposite sideline).
To be in tip-top basketball shape (at high school level), the player should be able to do this in under 1 minute.