From the Super Mario Wiki
A Backflip Block is a type of Block that first appears in Super Mario Run. They have a similar appearance to Long Jump Blocks and Pause Blocks (when the player is standing on it), except they are colored blue with a red arrow. When the player taps the screen while running across these blocks, they will perform a Backflip, which can be helpful in collecting Color coins if the player missed them. Similar to the Long Jump Block, players can press and hold the screen to perform a bigger Backflip.