There is no offside rule in the sense that the term is usually used in soccer and Ice Hockey. It is not necessary that the defenders have one or more men between the ball and the basket.
However, there are other rules to regulate player positioning. The over-and-back rule requires that once the attacking team has moved the ball into their opponents' half of the court, they may not move it back to their half again. This concentrates the action nearer to the basket. The "no camping" rule declares that no defending player may spend more than three seconds within the lane at a time, so the defenders can't just "camp out" under the basket to prevent shots on it. Hence all the inefficient-looking jockeying for position under the basket.
Sports such as ice hockey, Field Hockey, American and Canadian football, soccer and Rugby have an offside rule.
Futsal is governed internationally by the Futsal Laws of the Game, curated by IFAB, the same group that curates the Laws of the Game for Association Football (soccer). There are 17 Laws, although one of them (Law 11) simply states that there is no Offside. The basics of the game are identical to soccer, except in the dimensions of the court and markings, number of players and substitutions, the goal clearance, accumulated fouls, offside, the ball, and timing of the match. There are a few other differences, but they are mostly consequential to the other rule differences.
Futsal was created in 1930.
Nidaros Futsal was created in 2003.
Marca Futsal was created in 2005.
Liga Futsal was created in 1996.
Futsal-Liiga was created in 1998.
WAFF Women's Futsal Championship was created in 2008.
There is no BMI requirement for futsal. However, futsal is a fast sport requiring speed and agility, and most futsal players are built much like soccer players are.
Israeli Futsal League was created in 1998.
Uzbekistan Futsal League was created in 1996.
NFF Futsal Eliteserie was created in 2008.
Albanian Futsal Cup was created in 2011.