Rotgarth the Orc Barbarian wants to break Anne the Purple Dragoon's halberd (he's probably tired of all those polearm master's AoO).
Looking up the rules for objects, Rot can see that the halberd's shaft is:
Made of wood (AC 15)
Medium sized (some 8' long maybe?)
Probably Resilient (18 HP) those cormyrian halberds are made to last. That is why they sell so fast...
Rot is really excited. The halberd shaft probably won't resist a couple blows from his greataxe, specially in his raging hands. Grummsh be glorified, but...
How does one goes about attacking an object in possession of an enemy?