In this game a lot relies on your strength. Your rank in the memberlist depends on your strength. You possess attack and defense strength. Your attack strength is, as the name implies, important for attacking other players. Your defense strength plays a role in defending attacks from other players.
You gain strength by purchasing things like weapons, vehicles, etc. You can also work out in the gym or the boxing school
Boxing strength is required to beat other players in the ring. Of course, your boxing strength is also part of your overall strength. Boxing is only available to VIPs.