In the third stanza, MacCaig becomes more reflective and asks the reader to put themselves in the place of the cop and the people he comes into contact with.
The undesirable challenges the policeman faces are captured with a rhetorical question, in which MacCaig asks:
who would be him, gorilla with a nightstick, whose home is a place/ he might, this time, never get back to?
In this sentence, the nightstick refers to the baton that he carries, and this re-enforces his vulnerability against the power of the clubbings and gunshots that are referred to in the previous stanza.
The nightstick suggests a more basic and direct physical violence than a gun might. One can imagine the cop hitting someone repeatedly. This rhetorical question, designed to challenge the reader, makes one consider whether or not they would be able to do his job.
The poem ends with another rhetorical question, with MacCaig asking:
and who would be who have to be his victims?
Here, MacCaig considers two points in the same question – what kind of people would mess with the policeman, and what would they have to do for him to turn to violence (have implies that, though he is often faced with violence, it might be a last resort for the policeman).
The use of the word victims here is interesting, and MacCaig is perhaps suggesting that someone who gets on the wrong side of this policeman will be the victim. It isn't just the cop who is at risk of violence. The cop himself can act violently.
In the closing two stanzas, MacCaig shifts from a descriptive to a more reflective approach. Having described the policeman and his challenges, the closing two stanzas reflect on both of these.