Major Reversals are the Orange coloured reversals that occur when your opponent goes for a powerful grapple or finisher. To get these, you must wait for a green coloured (minor) reversal to pop up and reverse then (RT).
These reversals are more common towards the later moments in a match, so it may take some time for one to appear. Finishers are a great time to get these, especially against someone like Dean Ambrose, whose Dirty Deeds DDT I found quite easy to reverse. For them to get finishers, he would need to dish out some damage, so be prepared for that
Once you reverse the third major reversal, the achievement will pop