What is lacrosse?
Lacrosse is the original and oldest sport in North America.  it is one of the national sports of Canada.  It was created by French-Canadian Jesuit missionary priests in Canada, in the 17th Century.  The game of lacrosse is based on the traditional Native American game "baggataway."'  This means "little brother of war;" it was also commonly referred to as "The Creator's Game."  There are currently three predominant versions of lacrosse: Field Lacrosse, Box Lacrosse, and Women's Lacrosse.  
Field lacrosse is the men's outdoor version of the game.  There are 10 players on each team, on the field at once.  These players consist of 3 attackmen, 3 midfielders, 3 defensemen, and one goalie.  Each player has a helmet, shoulder pads, gloves, elbow pads, and a lacrosse stick.  6 players carry a short stick, which measures between 40 to 42 inches, and a maximum of four players on the field at a time can carry a long stick, which is between 52 and 72 inches long.  Short sticks are generally used by offensive players, and long sticks by defensive only players.  The goalie has a specific stick to his position, with a. wider "head" to assist in making saves.  The ball for play is made of solid rubber, about the size of a baseball.  A lacrosse goal measures 6 feet by 6 feet.  Teams are awarded one point for getting the ball into the goal.  
Each game is 60 minutes long, made up of four 15 minute periods.  At the start of each period, and after ever goal, there is a face-off at the center of the field.  A unique aspect of lacrosse is that on a shot, when the ball goes out of bounds, possession is awarded to the team closet to the ball when it went out.  On out of bounds other than a shot attempt, possession is awarded to the opposite team that touched it last.  During the course of play teams may substitute players "on the fly," through a designated substitution area (commonly referred to as "the box"), which is in between the benches of both teams.
Penalties in lacrosse result from rule violations, deemed by either an infraction (commonly referred to as a "technical foul"), or a personal foul.  The result of the offending team is either losing possession of the ball, or temporarily losing a player for a designated period of time (similar to hockey).  The offending player serves their penalty in the box.  The team that has taken the penalty is the playing "man-down" for the time serving portion of the rule violation, while the other team is player "man-up."
The generally consensus for who the greatest lacrosse player of all time is usually between three players: Jim Brown, Gary Gait, and John Grant.