Keylight problem

Hello, So first off my skill set is not based in after effects so this might be a simple fix....

I'm working on a side project where i need to do a High school soccer team lineup. The players are going to be placed in front of the school's green screen, and then squeezed back onto a plate of the soccer field for the starting lineup. Problem is i cant get a good key with key light. All it does is turn the green wall black....

Any tips or suggesstions would be appreiciated.