&quot;Set upon&quot; can mean either &quot;to begin to attack&quot; or &quot;to cause to begin to attack&quot;, although in the latter case the target of attack goes between &quot;set&quot; and &quot;upon&quot;:<p>The dog set upon the cat.  (began to attack the cat)<p>The person set the dog upon the cat.  (caused the dog to begin to attack the cat)<p>The second meaning could make sense in the original sentence with John being the attacker, a date (fruit) being the target of attack, and an unspecified party being the one who caused John to attack. In this case there is a past-tense passive with &quot;was&quot; + the past participle of the verb (like &quot;was liked&quot;, &quot;was seen&quot;, &quot;was taken&quot;), but the past participle of &quot;set upon&quot; is identical to the present form, so &quot;was set upon&quot; means <i>either</i> &quot;was attacked&quot; or <i>was caused to attack</i>. But only the second meaning is plausible when followed by &quot;a date&quot;, as opposed to &quot;by a date&quot;.<p>&quot;John was set upon a date&quot; → John was caused to attack a date<p>&quot;John was set upon by a date&quot; → John was attacked by a date<p>This reminds me that phrasal verbs really are one of the trickiest things in English. Some of my non-native speaker friends have several books just about this topic, because it&#x27;s so subtle and pervasive in English.