Each player has a shield that fills up from 1-3 segments each time damage is done to the player.
There are 8 segments in the shield in the current version of the game(There used to be 10[There also used to be a random Super Block that was removed]).
When all the segments in a shield are filled, the attack is blocked and the player gets a super-power that can be used immediately for free, or saved for later.
The shield then starts fresh up to two more times.
You can see the shield on the top right hand corner around where your life is indicated, and on the shield there are 8 segments. You can also see 3 small shields below it. Each time a block happens, it uses up one of those shields. After the 3 shields are gone, you'll notice that the heart with the life counter has no shield around it and that means that all damage is guaranteed to hit.
