Madara gets blind sided, he's trying to create barriers to stop Gai's attacks—does so in the first instance—and isn't able to keep up with Gai's speed and is slammed before he can make a full on barrier.
Gai's hammering him while Madz is trying to put up a shield.
Gai's hammering him while Madz is trying to put up a shield.
As I said, Madara was able to react to all of Gai’s initial attacks. When Gai does a combo, which means he forces Madara to do something first, then follows up with something else, that’s not just reaction to movement speed anymore. Madara got hit with the 2nd punch, because he’s still holding the barrier against the air pressure of first punch, as you can see in the panel.
Madara even reacts to Minato’s FTG attack, which is faster than 8 gates Gai.