How did Jared Padalecki break his arm?

Answer 1

Jared has broken both hands not his arm. He fractured his right hand in a bar fight during S1 filming when he and Jensen were jumped by a group of drunken men. He also broke his left hand near the wrist while filming Season 2 "Bloodlust" in the scene where he was hit on the head with a telephone and fell to the ground. The break was written into the plot of the Season 2 episode "Children Shouldn't Play with Dead Things" explained by his being tossed around by the zombie.

Answer 2

Episode 2.4, Children Shouldn't Play With Dead Things. In the scene where he gets chased by Angela, he fell while running and broke his wrist trying to catch himself.