Spock's eyes flicker to the ensign. He has several options. Try to reason with an unreasonable man, stun him, or find a way to redirect the aggression. He has no desire to add to the body count that Khan has already racked up in their timeline. Further endangering any form of the Enterprise is something the commander will not allow to happen. "Then properly direct that right at me." He states, affirmatively.

No sense in keeping his distance this will get ugly. There is no chance that it won't. He pulls out his phaser and points it directly at Khan. "Put the man down, and I don't have a reason to use this." It does not matter that it won't work or that Khan has the physical resistance to nullify the effects. It does not matter that Spock has minimal chance of success.

One thing he has learned from their encounters is that violence is unfortunately necessary.