Maniac is not played against opponents, rather Medals are earned by getting point totals. Earning points in Maniac Mode works a lot like earning Boost (which you still do in this event); Driving on the Oncoming Lane, score Near Misses, Drift, and getting Airtime all earn points. The final method is by performing Burnouts, which not only add points, but (if you are using Supercharge Boost) you will also get a Multiplier for every successful Burnout Chain. Crashing will not cancel your combo score, rather it'll automatically add it to your total score. This is much like stunt run in Burnout Paradise.
Maniac events are also done under a time limit. Players can extend the time by reaching a certain point total, however World Tour Maniac events only allow you to extend the time limit a certain amount of times. Also, Maniac events always last only two laps of any given track. This is again much like Stunt Run in Burnout Paradise.