Term for asking crowd to cheer louder

Solution 1:

Pump up the crowd.

An action where you put your two arms out to your side and curve your arms and scoop your hands inwards as [you're] flapping your arms up and down (Urban Dictionary).

Click here for examples: https://giphy.com/explore/pump-up-the-crowd.

Link to Joe Bolden Pumping Up the Crowd.

Link to M-W's definition of pump up.

Possibly related to pump up the volume (meaning increase the volume).

Solution 2:

They are egging them on to yell louder. I cannot find the origin but that is one use of it. To get the crowd aroused the player is said to be rousing the crowd.