One person throws strike, another applies basic counter,
then continues with strategy, going inside to out, or
reverse, OR continues with his own counter-attack further
with target of skull or knee or doubling up on same arm
that he blocked initially.

Practice this at medium speed to get control and understanding
of the lines.

Then, also, as the 2nd person is countering your strike
that you delivered, you disturb his counter, and let him
figure out the solution.