We know that there are 66k teams (coaches) in 131k schools in US (kids under 18). Kids under 18 playing basketball is just 14-20% of all basketball players, but elders don't have time to train, so we assume that the most trainings work with players under 25. So we assume that the full amount of coaches is 66k/0,5 = 132k. US is 26M/450M = 5.7% of all the basketball in the world, but affinity is ~2x higher than in other world, so globally we have about 132k/2/5,7% = ~1,3M coaches.
https://www.nabc.com/about/index
Let's calculate the basketball coaches market size in $.
The average coach has about 20 players in 1 team and up to 3 teams per coach. So there are about 132k * 20 * 3 = 8M players training with a coach 8M/26M = 30% of all basketball players in the US.