Until the 1930s lacrosse was mainly just played on large outdoor fields. During the summer the ice hockey arenas where mostly not that much used which made the owners think how to fill them in this gap times as well. So they rezised the field and changed the rules a little bit. Box lacrosse was born.
In 1987 the professional man’s box lacrosse league was started.
Box lacrosse is played with two teams of six people on a hockey rink. The ice on the rink is removed and artificial turf is used to play on. The enclosed playing area is called a box. Compared to field lacrosse, box lacrosse is a much more physical game.
Since cross checking is legal, players wear rib pads in addition to the shoulder and elbow pads that field lacrosse players wear.
The players wear a different type of helmet as well, a hockey helmet with a box lacrosse cage.
There is also a penalty box where the offeding player will be send to for a short amount of time and this persons team has to continue playing for this time without the offending player.
Within europe it gains more and more popularity.
The rules can be found here:
FIL mens indoor lacrosse rules