Good to hear you found it yourself (it's actually a bindable key-binding in options)
But next time, make sure to just edit your post, since it was only 2 minutes, and nobody in the mean time has posted here
FYI
Tab - disables ranking board
Shift + Tab - disables HUD (score/Combo/acc etc.)
H - (in replays) disables those replay buttons (like fast forward, discussion etc.)