You don't think the bloody nose and being shoved in addition to that will be enough?
A little research on my end shows that Oklahoma does have stand your ground laws, which may make this enough for him.
Here's what I found for a code section:
A person who is not engaged in an unlawful activity and who is attacked in any other place where he or she has a right to be has no duty to retreat and has the right to stand his or her ground and meet force with force, including deadly force, if he or she reasonably believes it is necessary to do so to prevent death or great bodily harm to himself or herself or another or to prevent the commission of a forcible felony. 21 O.S. § 1289.25(D)
So I guess it doesn't come down to the duty to retreat in Oklahoma, but more it comes down to whether he reasonably believes it necessary to prevent death or great bodily harm. That's where I think his case becomes tough, because with a bloody nose and a little shove I'm not sure you can say that force was necessary to "prevent death or great bodily harm."