I think this is an aspect of the turn rules, and it is incumbent on the defender to react it their turn to drive off the enemy cavalry attacking his infantry, perhaps from a source other than the adjacent cavalry.
Personally, if I was the original attacker, I would likely attack the defending cavalry first in an effort to write them down, rather than an infantry unit that could square up, and bounce my cavalry attack.
So in short, I don't really see the need here, and my reactive cavalry is often back further, ready to counter attack cavalry incursions.
Glory is fleeting, but obscurity is forever.
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