The use of a cross man defense can be very beneficial in stopping crossing routes or drag routes. Often you will only be able to cross man with your two safeties or your middle linebacker but it does depend a little on the defensive formation you are using.
Let’s go over it step by step.
Step 1: On defense before the snap press Y/Triangle to bring up your defensive adjustments
Step 2: Then press Y/Triangle again to bring up your quick adjustments
Step 3: Press the button that correlates with the safety you wish to Cross man
Step 4: Press up on the right stick to select man coverage
Step 5: Press the button that correlates with the offensive player you wish to man the defender too
Basically, what you will be doing (for example) is manning up the left side safety to a receiver on the right side of the field. Then manning the right side safety to a receiver on the left side of the field.
You could see how this would be very effective at taking away routes over the middle of the field but it does leave you vulnerable to any sort of route toward the sideline.
This is an advanced technique so only try it if you really know what you are doing. If you do it poorly, you could be giving up an easy touchdown.