Will waivers protect us from liability during a staff trip to the ballpark?

Q: “We are taking our staff to a baseball game for Staff Appreciation Day. It is completely optional, and they can choose to remain at work or take a leave day if they don't want to participate. Question: If one of them should get injured during this event, is the organization liable (through workers’ comp, etc)? If so, should we have them sign waivers before the outing that would relieve the organization of liability?”—S.N., D.C.