Why does my fan go crazy when I command-tab out of a game and how do I fix it?

My fan is perfectly fine while running a game (such as League of Legends) even if I am playing for hours on end, but my fan goes crazy (starts getting REALLY loud) when I command-tab out of it. The fan goes back to normal after a few seconds of command-tabbing back to the game. Is this something that I can fix? It is really annoying when I want to command-tab out of the game for a few seconds to quickly respond to an email or check my facebook and hear the fan get extremely loud in that short time. I'm not sure if it will help but I have attached my Mac's specs just in case. If there is any other information I need to supply please tell me. Thank you so much in advance!