Kinect Sports Rivals

Getting close to a mine, without actually hitting it, activates it and causes it to explode two or three seconds later, with the intention of catching an opponent in the blast radius.

Although activating eight under race conditions is perfectly achievable, this is easier to do on a specific run. Take it slowly, by opening up your throttle hand instead of closing it like a fist, and make sure you get your aim right. You have to get pretty close to activate a mine, so doing this in a race you're trying to win will usually result in hitting one or two in the process, ruining your chances of coming in first place.

I chose the second course you do, after you've done training, and gone through the set of challenges the three teams set you, and you have to catch up with your 'coach' before choosing a team. There's a reasonable number of mines, and they're laid out in a way that they're relatively easy to activate without blowing yourself up (although, as Iron Man TStark and QuickMythril point out, getting blown up doesn't invalidate the achievement, as long as you get the game to register the activation of the mine first).

There's no time limit, so take it easy and get your jet-ski at the right angle before opening up the throttle.