your presuming it happen the way the off duty guy reported it.
Blood half the way up the street and only then did the guy pull a knife and cut one of them. If 4 Fijian Scottish regiment rugby players decide to kick your head in your going nowhere after the first punch has been thrown.
More like the insult was given the lads turned towards him. He announces he is a cop and pulls a knife. That doesn't stop them. They advance and he cuts one of them and then realises that they are really not bothered by a blade. He legs it and the blood up the street is the solders blood that got slashed chasing. They catch him and beat him up.
But we will have to see what there side is.
The mobile phone theft is the big issue and indefensible.
Anyway we shall see what colour the judge is and if there is CCTV
I expect the cop is going to have an interesting time at work when he goes back.