The lastclap is a maneuver used against a shardbearer, commonly by those who are unarmored and unarmed, as they have no other way to fight back. The lastclap can only be done when the shardbearer attacks in an overhead swing.
During a highstorm, Sylphrena warns Kaladin that the "One who hates" is coming. Kaladin, who also has the impression that something is wrong, hurriedly gathers Elhokar, Dalinar, Renarin, and Adolin. As he is escorting them to safety, they enter a hallway that is dark, since the stormlight that gave it light was taken in by the Assassin in White. Dalinar, Adolin, and Kaladin attack, Renarin continuing on with Elokhar. Adolin is lashed to the ceiling and Kaladin is hit in the arm with Szeth's shardblade, rendering it useless. Dalinar is trapped, and when Szeth strikes an overhand blow, Dalinar brings the palms of his hands together as the blade falls and catches it. This defense is called the lastclap.
”Old Dalinar pulled off a lastclap, eh? Good for him.
After the fight, Kaladin asks for Zahel's help in fighting a shardbearer. Zahel agrees, and Kaladin asks if Zahel can teach him the lastclap. Zahel responds by saying that it is a "stupid maneuver" and that it only works when shardbearers swing overhand. He also says that it usually fails, and then "you're dead." He urges Kaladin to focus on other strategies that work more often, and Kaladin agrees.