The paintball gun (marker) with an attached compressed air tank is the most essential piece of equipment to the player.  This gun can electronically fire paint rounds up to 20 times per second in semi-automatic mode.  That means the person firing the gun must pull the trigger one time for each paintball to fire.  Each time the player pulls the trigger, an electronic solenoid opens and releases a small amount of compressed air from the tank to accelerate the paintball down the barrel. 

In addition to the gun, you need a hopper to hold the paintballs during the game.  This hopper hold up to 200 paintballs.  It forces the paint into the marker with a motorized feed wheel activated by an infrared laser.  Standard gravity fed hoppers will not sustain guns that are capable of shooting 20 balls per second.

The last critical piece of equipment is the paintball itself.  Manufacturers produce the standard .68 caliber size paintball with varying colors and thicknesses.  The recreational player wants a thicker more reliable shell, while the tournament player wants a thinner shell to ensure breakage on anything it contacts.  The filling in paintballs is 100% non-toxic made with various dyes and fish oils.  Manufacturers make tournament fills thicker thus easier to spot and recreational fills thinner thus easier to clean. 

I labeled the above 3 pieces of equipment as essential because if you went in your backyard to shoot at trees those are all you would need.  However, if you plan on playing against other people, you must where a mask.  Most fields enforce a maximum speed of 300 feet per second.  That translates to around 200 miles per hour.  At that speed, a paintball could easily take out an eye.  Just like any other sport, paintball can be incredibly dangerous if the proper safety precautions get overlooked.

Other optional equipment

                                      
Pants                           Jersey                           Gloves