There is the option to flip the other over his shoulder - he's strong enough, both from working out so often and from the new Augmented blood (he had noticed a slight strength increase, but to be honest he tried not to think about it). No, he had something else in mind. Flipping someone took a lot of effort, and if you weren't strong or had much weight, it could be difficult despite the momentum. The idea of self-defense was to defend, but that could be taken several ways depending on situation and your own personal strengths.

So instead of flipping Sam, he waited for him to come just in reach and slid just a half step to the side. He reached out to take his arm, redirecting Sam's momentum so that he slid past Kirk to lose his balance and be forced into the dirt - or at least try to force him into the dirt. A person could recover from the stumble, but even then if they just charged again the move could be easily repeated until they fell and the defender could make a break for it while the opponent recovered.

In this case, Kirk took the chance to dance a few more steps away and well out of Sam's immediate reach regardless of a recovery or not.