The first thing you’ll be told in a flash photography lesson is “... get the flash off the camera ...” – as this will create directional light, resulting in images with “ ... mood, texture and dimension...” (as Cliff Mautner so elegantly states it).
But what if you can’t take the flash off the camera? – photographers would normally then resort to swivelling the on-camera’s flash head backwards or to the sides to bounce the flash off a wall or ceiling - but as a sports photographer out on the field (with no walls or ceilings), things happen quickly and the post match celebration and jubilation moments last for a short time only.
In the example below, I used an on-camera flash, with a diffusion dome light modifier attached. Flash was set to TTL / BL mode angled upwards at 70 degrees which produced a sliver of soft feathered light – so even with an on-camera flash, on those occasions when you can’t get the flash off the camera, using this technique, you can still create some texture and dimension and get those important catch lights high up in the eyes.
(Credit to Cliff Mautner for showing this technique in one of his classes)