Let F be the number of shots Jordan blocked in the fourth period.
In the second period, he blocked 2 * 4 = <<2*4=8>>8 shots.
In the third period, he blocked 8 - 3 = <<8-3=5>>5 shots.
In the whole game, he blocked 4 + 8 + 5 + F = 17 + F = 21 shots.
Thus, Jordan blocked F = 21 - 17 = <<21-17=4>>4 shots in the fourth period.
#### 4