Hardy - who has starred in Taboo, The Revenant, Mad Max and Legend - threw the alleged thief into a bus stop before patting him down for weapons and checking his ID.
Arun Pullen, 22, told The Sun: "It was mental - like he'd switched to superhero mode in an action movie. "Tom Hardy's clearly not a man you'd mess with. I think he even checked the kid's ID before cops took over."
Witnesses claim the actor said: "This little s*** nicked something and now he's got himself a broken leg."
According to The Sun, two men were riding the stolen bike which crashed into a Mercedes. Both were injured and one was caught by police while the other fled the scene - before being caught by the actor.
Both are reportedly facing theft charges.