Could even argue GBH given he's had a need for stitches, it was pre-meditated, and the alleged assault was directed at the head. Flip side, no weapon & very quick incident.
But yeah, I suspect a charge of ABH or a charge that is eventually pleaded down to an ABH, at least.
Guilty plea at the earliest opportunity, knock a third off any sentence, clear CCTV evidence (+ a witness or two) militates in favour of that.
Probably passes the custody threshold, even with an early guilty plea.