NJ, the chap he was apparently defending himself against was also acquitted. A fellow cricketer who was (allegedly) on the video kicking an Afghan veteran in the head wasn't even charged. It appears the CPS also tried to add a couple of assault charges once the trial began, but was refused (I'm not surprised, they'd had almost a year to sort their charges out).
So all in all, seemingly a drunken street brawl in which no laws were broken. Or maybe, as PP suggests, simply one for which the prosecution wasn't up to it.