Press the button to start sprinting.
While you hold it down, you're in SMART mode.
In this mode, when you run at an obstacle, you'll automatically climb/vault/mantle over it instead of getting stuck.
If you're Heavy, you can only SMART over waist-high objects, Mediums can quickly climb eye-level barriers, and Lights can wallclimb things up to a storey tall (and can use wallhops to get at places higher than that using manual controls).
Yay, new info I didnt't have
they say you learn something new everyday, i just dont think i ever expected to learn something 5 minutes to midnight lol
I'm pretty sure the devs said that it was on a shoulder button, but again, this is irrelevant because the controls for all versions are completely mappable. On top of that, they actually imported control schemes of some popular games, which they don't recommend you use, but it's an option.
Thanks to this, I now know several more people i can convert to BRINK
bliviongate: lol
On top of all that, yay to mappable controls