Coming on Strong Achievement in MX vs. ATV Supercross Encore
Coming on Strong15
Lap an Opponent in a Race
How to unlock Coming on Strong
This is easiest to boost with a partner (recommended if you've buddied up to boost other online achievements as it will only take a moment) or by increasing the laps to 6-10 (higher if you feel necessary) when versus an A.I. opponent on Rookie difficulty in a Single Race. I also found during a handful of races on any of the 450cc championships that some of the AI would fall so far behind on the Rookie difficulty setting that you could lap them, so it may just come naturally.