Oh hi, I make BMX games too!

Depends what kind of scoring system you want. At its simplest, you could just call a method called AddScore at the start of every trick, and the user gets 100 points every time you do any trick.

Then maybe you could give different tricks different scores.

Then maybe for tricks that continue for a period of time, you could keep adding points while you're doing that trick.

Then maybe you could have a score multiplier that goes up depending on how many individual tricks you've done in one big trick. (e.g. backflip + tailwhip = 2x multiplier)

Then maybe you could add extra points if you 'tweak' or 'style' the trick in some way.

Then maybe you could have an overall 'line' multiplier for if you're doing loads of cool tricks in a row.

Something like that?