Believe it or not, there are hardcore laser tag players who fight to the death in abandoned military bases, using incredible, highly modified custom guns.
To start with, you will need a microcontroller, a photoresistors, and plenty of cheap laser diodes with collimators lenses. By using the photoresistors to have the microcontroller learn your lasers signal, and then reproduces that signal at the press of a button. The trigger for firing the rockets is actually from an actual tank.
And put all the lasers facing outward in a ball and presto, a laser tag grenade. To fire the rocket, the player has to hand pumped the gun to pressurize a plastic pneumatic tank.