Maybe u forget to attack ur opponent after ducking so it doesn't improve.
Or, if u currently playing in Easy difficulty, strike ur opponent once to incite him to strike u. There's always a delay before they begin to strike (in Easy). They walk closer 2 times 'n then they attack. If ur opponent has stopped walking closer to u by twice, wait until they start attacking (at the moment they move their arms) and press R2 to reverse it. Try this trick, it's useful! It has a success rate of approx. 92.