Bruce is laid up, could be illness, could be injury, could be a business trip, up to you. Justice League volunteers to patrol Gotham and figures it'll be a piece of cake if they all do patrol. Cue the League getting a real wake up call into how rough Gotham is and the criminals not being impressed with the Justice League.
Bonus points for: 'That's cute, Boy Scout. Where's Batsy? He at least knows how to play.'
Bruce Wayne/Justice League - Gotham Villains Prefer Batman
Bonus points for: 'That's cute, Boy Scout. Where's Batsy? He at least knows how to play.'