Without the tug and flow of the Force guiding his focus, Kylo barely hears Ronan's voice. His attention, all of it he has available to him, is on the figure straightening up from a crouch on the ground— right where he needs it. With his senses pared down and supplying only such basic, immediate information, he doesn't have anything left to spare.

If Declan won't leave, Kylo's mind supplies him, if he can't or won't stop, then he has to be stopped. The threat ends with Declan unconscious and unmoving. Nothing less.
And so this time, no longer offering an alternative, Kylo hurls himself at Declan not with the intention of driving him off but taking him down, his arm swinging heavy for a brutal blow to the jaw.