Trapdoor fractures, or blowout fractures, result from muscle entrapment after orbital floor fractures. The incarcerated muscles may become necrotic because of ischemia; immediate surgery is recommended for symptomatic persistent diplopia or clinical evidence of entrapment. We report a case of spontaneous resolution of diplopia in a patient with a high suspicion of a trapdoor fracture. A 15-year-old girl presented with diplopia after being hit in the eye while playing volleyball. Computed tomography did not show a fractured orbital bone, but the forced duction test was positive when the left eye was pulled forward toward the left. Magnetic resonance imaging was negative for edema and inflammation in the extraocular muscles. With observation only, the diplopia resolved 2 weeks after onset. A negative forced duction test confirmed the resolution. Observation only may be appropriate in cases with posttraumatic limited ocular movement, after imaging has excluded an emergent condition.