Ash have higher AP and durability which is his major advantage because he can literally overpowered Ritsuka with his sheer strength alone. I don't know the calc for Ritsuka but a navel gun in middle of 17th century can deal
this much of damage, although that won't cover his disadvantage in physical stats. However, that is all Ash have so i'll move to Ritsuka next.
It's undoubtedly that Ritsuka is far more skilled than Ash is, he have been trained by legendary figures and so on. Honestly, why don't he have Martial Arts or something similar in his profile? Also his stamina should be upgrade as well given that he've went through some extreme training under Scathach, Leonidas but its a different matter for now.
Considering the situation this is basically skills vs AP at this point, all Ash can do is trying to punch Ritsuka to death or choke him into submission. Let take a note here, we cannot determined how skilled Ritsuka is as a fighter, mainly because he haven't been an direct combat for most of the time. However we can't disregard the training he've received, Ritsuka would know how to dodge, to analyse situations and when or where to strike at his opponent. It may seem like i'm overestimate him but it's true, in martial arts, military or any kind of combat training they are basic knowledge that everyone must known and learnt. While Ash feat may have his fair share of knowledge in tactical combat and being an athlete himself, Ritsuka being throughly trained would give him the edge in this field.
Ritsuka would spend a few seconds analysing his opponent and after a few punch and kick, Ritsuka then realized that Ash is physically stronger than him so he took few steps then go into defensive position. He know that his normal attack won't work so he'll target his vital points instead, repeatedly poking his eyes will lead to wound being fester and worsen over time.
As for Ritsuka's Social Influencing, everybody already explain it so i won't tap into it much. I do think that it is possible for Ritsuka to convince Ash to surrender and it doesn't take a genius to accomplish it, a person who having a way with words can easily do that. We've seen Ritsuka dealing with psychopath and maniac on daily basic so Ash shouldn't be much difficult.