Key Clinical MessageSudden onset bulging of the upper arm may indicate biceps tendon rupture.AbstractWe describe a 72‐year‐old man with Popeye's sign. The patient experienced a sudden shock in his right humerus while mowing grass with his right arm using wide sweeps of a scythe. His right upper arm had an obvious bulging appearance after 3 days, indicating a rupture of the biceps tendon.