Pursue QB (button)?

Was watching the MCS stream last night and the play by play guy said something about a pursue QB button. I don't remember exactly what or how he said it but it was something to the effect that: you have to know when to time that button as the lineman will crash down towards QB (like when the QB is on a roll out). For the life of me I can not find the button he was referring to. Anyone know what he was talking about? If so, how and when is this button used? I think he said it was one of the stick buttons but I could be mistaken. 

Thanks in advance.

Press down on the left stick when the play is going and the nearest defender to the QB will pursue

Ah, So pressing down on left stick sends closest defender towards QB, not the defender Im using , gotcha. Thanks for the info.

JJ18 said:

Press down on the left stick when the play is going and the nearest defender to the QB will pursue

Why not use a spy then? Shouldn't they all of your blitzers be pursuing eitherway?

Rocketv2 said:

Why not use a spy then? Shouldn't they all of your blitzers be pursuing eitherway?

People often use spy’s to avoid getting locked into blocks, follow the QB outside of the pocket without getting blocked then click pursue QB and the spy goes unblocked to the QB