This the typical outcome of territorial outside cats. They like high plays so they like to be on roofs but when a cat intruder arrives they might fight on the roof which leads to an inability to observe that they are about to fall off it as they are so obsessed with fighting each other. There is an intense singlemindedness in the domestic and stray cat territorial fight. It is very viscious.
They fall on soft ground thankfully. They were probably unharmed by the fall. If humans fell that far and landed on their side they’d probably be badly hurt.
The fights often lead to head wounds. Ears are torn and obsesses form under the skin of the skull. These are all typical fight wounds.
To cap it all, after they fall to the ground a small terrier dog happens to be nearby and attacks one of the cats who fights back and then runs off.
These cats put themselves at risk of severe injury in their compulsion to protect their home which is a patch of ground perhaps about 3-4 acres in size or thereabouts.
They probably normally avoid each other through marking the boundaries of their home range with urine and cheek scent marking. This is their calling card and it tells intruders where and when they were there.
But occasionally they bump into each other and bingo, it’s almost a fight to the death. It is looks very irrational and pretty pointless because they could live harmoniously. People struggle to live in harmony too.