The longer version
Occupancy is booked hours divided by bookable hours. A club with 4 courts open 14 hours a day has 56 court-hours daily. If 38 are booked, occupancy is 68 percent. For classes it is spots filled divided by capacity. Court blocks are usually excluded from the bookable total so maintenance does not look like missing demand.
Clubs care because occupancy is revenue and shows where it is missing. Overall occupancy hides the story: 95 percent at 19:00 and 20 percent at 11:00 is a pricing problem, not a demand problem. The useful view is occupancy by hour of the week, by court, and by season.
The mistakes are counting held or unpaid bookings as occupied, comparing against opening hours the club never actually sells, and reading a single week. Use paid bookings, the real bookable grid, and at least 4 weeks.