Peacekeepers under attack left boxed in without a strategy (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

UN (abbreviation for United Nations: often “peacekeepers” in crosswords, though that’s a slightly narrow definition of their remit) + PANNED (criticised harshly = under attack, as in “the film was panned by almost all the reviewers”), with L (abbreviation for left) inserted (boxed in).