During FNM Player A is the active player and is playing infect. Player B is playing U Tron. During the declare blockers step Player B as if Priority is based and tries to move to combat damage. Can Player A say no and cast spells before combat damage is assigned since Player B didn't do anything after priority was passed? Details in the answer would be appreciated. I'm asking due to how 500.2 is worded.
500.2. A phase or step in which players receive priority ends when the stack is empty and all players pass in succession. Simply having the stack become empty doesn’t cause such a phase or step to end; all players have to pass in succession with the stack empty. Because of this, each player gets a chance to add new things to the stack before that phase or step ends.
On player A’s turn, after B declares blockers, A will receive priority first. If A does nothing with that priority and passes it to B, and B also simply passes priority again then the game will proceed to the combat damage step and combat damage will be assigned and dealt before either player receives priority again.
What your question seems to be hinting at is that B is either trying to rush A through their chance to cast a pump spell or A is fishing to see if B has a removal spell or the like. Neither of these things are allowed. A should declare any spell or ability they want to cast/activate as soon as blockers are declared without taking an undue amount of time in which they can fish for a reaction from their opponent.
