Regardless of the sport, there are always some fans in the stands who will yell to players (yes, the professional athletes they paid to watch) to perform the most obvious fundamentals of the game.
Shoot! Swing the bat! Throw the ball! Tackle the ball-carrier! Don't let them score!
It really doesn't matter where you take in a game. Wherever you are, you are likely to hear someone yelling one (or more) of those things at the players. Because apparently, the athletes got to that level without knowing what to do during games.
Edmonton Oilers defenseman Andrew Ference put together an entertaining video for the CBC's The Irrelevant Show in which he facetiously thanks fans for shouting advice to him while he's on the ice. He also raises a good point by mentioning that fans yelling instructions can hurt their team—because the opposition then knows what's coming.
Now, it's up to fans to come up with signals so they can slyly let players know what to do during games.