Complex sentence: The version of lacrosse played in the NLL is indoor lacrosse, slightly different from box lacrosse, which is played on a hard floor, usually in the summer, and has 4 periods instead of 3.
Split into simpler sentences: The version of lacrosse played in the NLL is indoor lacrosse. This is slightly different from box lacrosse, which is played on a hard floor, usually in the summer, and has 4 periods instead of 3.