Simultaneous Defense and Attack
Block first, then hit, is one tempo. Block and hit in the same motion is half a tempo. That half-tempo wins fights.
Most traditional martial arts teach defense and attack as separate beats: block — then counter. Krav Maga teaches them as one beat. The defending hand redirects the threat while the other hand (or knee, or head) is already moving forward into the attacker.
The tempo math
If your opponent's punch takes 0.4 seconds and your counter takes another 0.4 seconds, a sequential defend-then-counter response gives him roughly 0.8 seconds to launch a second attack. A simultaneous defense and counter collapses both into the same 0.4 seconds, robbing him of the second shot.
How it's drilled
Beginners learn defenses and counters as separate movements, then are coached to compress them. By the time a student is graded past the introductory levels, the instructor will fail any technique that comes back as "block, then strike." The defense and the counter must leave the holster at the same time.
Edge cases
Against weapons — knife, pistol, long gun — the simultaneous principle becomes non-negotiable. There is no time for sequential responses against a moving blade. The hand that redirects the weapon and the hand that strikes the attacker move as one piece.