don't know if this can be done but...

rockcanyonphotos

shooting helmeted sports sun in bright overhead light. Has anyone ever tried to underexpose to the point where you can use a flash during the day?? Can it even be done?? Just a wild idea... you are all welcome to make fun of me :-)

TangoJuliet

I'm not sure about helmeted sports, but I've used flash during the harsh mid-day sun to fill in under hat brims with Canon ETTL II and a 430EX.

zoomer

Yes it is doable, you need a lot of flash power.