I might be long winded here but:
when using jostle/grab as a defender, you will still need to control your player with your L-stick and sprint is needed. this is not like holding "A" to contain which puts your guy in "auto-pilot". if you just stand there holding "grab" you will do 0 and the defender will separate from you.
using 'contain' attempts to have the CPU put your player in the best position to defend, as above it is a sort of auto-pilot. the defensive 'grab' is done in addition to your standard running/controlling of your defender. so you can be guiding your player using the L-Stick, holding sprint to keep up with the sprinting attacker AND holding 'grab' to attempt to pull back the attacker. remember there is also a difference between "holding" the grab button and tapping it as holding it down is to grab, tapping it is to slide tackle which can be a bad thing when chasing a defender...
normally if you are going to use the "contain" button, it is when you are in front of or in a decent defensive position. the "grab" button is more for when you are chasing the play and trying to get back into a better position.