Everything is legal in an illegal car race, but sometimes that doesn't mean that you need to do something harsh. Some of the guys racing there are also reputable and honest. Anyway, the general rule is not to do anything harsh unless you got provoke.
In this game, you don't need to worry about anything as you just need to shift the gear when it is time. However, that won't be easy since you need to shift the gears at the right time. It means that you need to take action not on or before the green light. Timing is very important in this game as that determines if you win or lose.