There are key moments in every game. We all know that.
In Dublin V Mayo 2019, the key moment was when Con O' Callaghan scored his first goal ( Mayo needed to stay in the game for the first 15 minutes of the second half). While Dublin did up the intensity in the second half, there were 3 factors that led to the first goal.
1 Ciaran Kilkenny's vision and ability to execute a long fist pass
2 The connection and awareness Kilkenny and O'Callaghan have of each others game
3 Lee Keegan's Poor Defending
While Mayo could not do anything about the first two factors, the third factor was a fundamental defending error. Lee Keegan was playing a yard on front of O Callaghan, which gave O'Callaghan the upper hand, as it was easy for him to loose Keegan for the split second required. It looked like Keegan's slip was the problem, but it was the fact that he had to over reach to recover from his bad body position that led to the slip.
If keegan had adopted a slightly different body position, this goal could have been averted.
Right hand on his back to feel his movement ( far harder for forward to loose the defender)
Chest on O Callaghan's Shoulder ( creating a barrier between attacker and goal
Left Hand Across O Callaghan's Body to knock ball away if required ( prevent the easy pass out in front)