The poem's first line reveals that the speaker is beginning in the middle of a conversation—some "occasion" has already been talked about, so now the speaker turns to "another" one. Immediately this makes the poem feel casual and conversational, as if the speaker were simply telling a story to a friend over a drink or meal.
Certain words and phrases throughout this stanza also suggest that it's probably a soldier talking, and that this story is about something that happened while the soldier was on duty. In line 1, for instance, the phrase "we got sent out" indicates the speaker is working as part of a team or unit, and that they are acting under someone else's orders. Line 2, in which these people then "tackle looters raiding a bank," serves to further confirm that this action is taking place in an area of active conflict. In general, "looters" would be the term ascribed to thieves pillaging buildings during war time.
These opening lines also introduce the colloquial tone of voice the speaker will use throughout. This is exemplified in particular here by the speaker's use of the informal "legs it up the road" in line 3, where "legs it" is a British slang term for someone running away quickly. In other words, the speaker is saying that one of the "looters," upon seeing the soldiers arrive, tried to run away.
The fourth line of this stanza sets up an important point of reference that will carry through the rest of the poem. The speaker states that this man was "probably" carrying a weapon, but also that he "possibly" was not. This matters because, as becomes clear later in the poem, the speaker is overwhelmed by the guilt of potentially killing an unarmed man. On a formal level, the reassuring "probably" is filled with confident, /p/ and /b/ plosives, but this is immediately undermined by the tentative "possibly," where the hissing /s/ sound lingers with doubt.
The phrasing of this stanza is is fairly disjointed. Line 1 is enjambed, its meaning stumbling across the line break ("we got sent out / to tackle"), and both lines 1 and 4 feature caesuras that force pauses mid-line. ("occasion, we" and "armed, possibly"). These stops and pauses seem to mimic the speech patterns of someone telling a story they are perhaps uncomfortable with, as they try to build up momentum in order to reach the part they dread having to say out loud. Even as the speaker appears to be casual, this halting rhythm already suggests this nonchalance might be an act—that the speaker is actually struggling to reckon with the truth of what happened.