1
general::
Phrase(s): set someone or an animal on someone or an animal
to command someone or an animal to attack someone or an animal. • The gang leader set his thugs on the unwary tourists. • Scott set his hounds on the raccoon., Phrase(s): set something (up)on something
to place something on the surface of something. • Mrs. Franklin set a bowl of fruit upon the table. • I set my empty glass on the counter.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Also, set upon. 1. Attack; see SET AT. 2. Instigate, urge one to engage in action, as in The older boys set on the young ones to get in trouble. [Early 1500s] 3. be set on or upon. Be determined to, as in He's set on studying law.
American Heritage Idioms