In football, controversy rages when it isn’t clear that the ball has crossed the goal line ‘with its full circumference’.
Leaving aside that the ball is unlikely to be exactly spherical when kicked, today’s invention is a low-tech way to remove any such doubts (FIFA is notoriously conservative about the adoption of anything newfangled, even when its absence makes this low-scoring game look ridiculous).
Instead of nets behind goals (which flap and raise more doubts about where the ball actually went) a flat sheet of perspex is fitted exactly one ball diameter behind the line. The sheet is provided with a weatherproof perspex box and coated with eg Vaseline or other waterproof gel (so the action can still be seen from behind the goal).
All this fits into a frame on the goals and would probably be no more expensive than nets anyway.
When a score is in doubt, the referee need only inspect the Vaseline on the sheet for any marks. If there are any, a goal is awarded and a new sheet slotted in.
Two such perspex sheets could be used even in Sunday league games with one sheet being recoated whist the other was in-goal.