To take your formations a step further in stopping the pass, it might be a good idea to manually play as a player in the secondary, instead of someone on the defensive line. Just press B, Circle until you're over the desired player you wish to control, and hold down the right trigger to bring up the player art, which will show what assignment that player is one. It's extremely important that you stick to the assignment, so if you're assigned to cover one player on offense, make sure you stick with them, and if you're in zone coverage, make sure to never stray outside of your given area. 

When user controllering a player in the secondary, it's very important that you make sure no offensive players get behind you. It's always a good idea to keep any players in front of you, as it's easier to  Madden Mobile Coins dart down the field and swat away a pass, than it is to catch up to a player who's behind you and try to bat down a pass.  

But when should you actually blitz in Madden 18? Blitz plays are generally designed to either stop the run, or to sack the QB before they have the chance to pass. Blitz plays are best called when you either want to make sure a running play never takes off, for example in short yardage situations on third or fourth down, or when you don't want to give the QB time to pass.