Apparently, the Philistines wanted to capture Samson alive, not dead. This is shown by the fact that when they finally did capture him they didn't kill him.So - get the 20 archers to all shoot him in the leg.
Would shooting Samson in a leg with several arrows render him weak and helpless? Even after the Philistines bored his eyes out it is reported: "the dead that he put to death in his own death came to be more than those he had put to death during his lifetime."
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