Ils (commencer) leur travail après la match de foot.

Explanation

The correct answer is commencent
The correct sentence would be: "Ils commencent leur travail après le match de foot." Which translates to "They begin their work after th football match."
The subject of the sentence is "Ils" (they), which is a third person plural pronoun, so the verb "commencer" must be conjugated in the third person plural form, which is "commencent".
Here's a breakdown of the other options:
commence (first person singular, "I begin")
commences (third person singular, "he/she/it begins")
commençons (first person plural, "we begin")
commencent