Yup already thought about that but IMO it's much more work and prone to errors compared to just installing some sensors. Want to get that running ASAP and after that we can look into CV options. Already found a project [0] that tried to accomplish that with OpenCV but it seems it's abandoned.
If you can track the ball reliably like the guy from Stuff Made Here does on some of his projects it would maybe be a first step? Anyway this sounds like a super fun project! Good luck!
[0] https://github.com/StudentCV/TableSoccerCV