After losing the Omnitrix, the Violet Offenders had robbed a bank. John gave chase using only his mana powers, and they were able to outmaneuver him and send him crashing into a truck.
John later encounters an alternate dimension version of them, and takes out his anger from the last loss out on them. He defeats them with ease.
After returning to his home dimension, John fights the Violet Offenders again, who are now working for Otto.