Tettsui-uke (literally: “iron hammer block”), the hammerfist block refers to the defensive applications of the hammerfist strike. Like their offensive counterpart, hammerfist blocks model the form of shutō blocks, and still contact the opponent with the shutō, even with a closed fist. Hammerfist block is a very diverse move, which can be executed in a number of directions.
Outside hammerfist block
To execute an outside hammerfist block, pull the blocking hand up to the opposite-side ear, with the palm facing inside. Cover your floating ribs on your blocking-hand side with the opposite-side hand. (This is the same position that downward-fist blocks are executed from.) Remember, everything must come in before it can go out.
Then, pull the blocking hand across the chest, until it is in front of the same-side shoulder, with the palm facing down. At the same time, chamber the opposite-side hand by pulling it across your waist to its hip, setting up a counterattack.
[Video of an outside shutō block, slow and fast, from the front and side]
Inside hammerfist block
Inside hammerfist blocks are similar to a tate shutō uchi or ude uke. Pull the blocking hand up to the same-side ear, with the palm facing towards inside. Then, pull your elbow across your chest, until your blocking hand is in front of your face, so you can see your own palm. Your shutō will swat your opponent’s attacks away.
[Video of an inside shutō block, slow and fast, from the front and side]
Rising hammerfist block
Rising hammerfist are just rising blocks which connect with the shutō of a closed fist, instead of the forearm.
[Video of a rising shutō block, slow and fast, from the front and side]
Downward hammerfist block
Downward hammerfist blocks are essentially downward-fist blocks performed to the side of the body. Downward hammerfist blocks are the most common defensive option used when fighting from side-facing postures (e.g., horse stance, or full-side-facing)
Downward hammerfist blocks are performed exactly like downward hammerfist strikes, but with the intention of swatting instead of crushing. To perform a downward hammerfist block, pull your arm back sharply, as far as possible. (Ideally, this is a rear elbow strike.) Then, straighten the arm out and down in a snapping motion. The forearm should not swing freely while the elbow remains fixed in place, like a folding pocket knife. The elbow should drop down as you perform a downward hammerfist, giving it the same crack-the-whip feeling as an outside hammerfist or a winding knife-hand strike.
[videos of downward hammerfists, fast and slow from the front and from the side. Also, show a bad example where the fists swings uselessly from the side, and shout “NO!” or something.]”