When you waylay someone, you stop them from doing what they were going to do, either by using violence or some other tactic.
To waylay, or to be waylaid, is usually not a good thing: Mom would not be proud. Robbers waylay their victims. Outlaws waylaid stagecoaches in the Old West. The verb's origin, from wegelage, means "lying in wait, with evil or hostile intent." You might also use waylay to show someone being interrupted from finishing the task at hand: "I should’ve been studying, but was waylaid by my friend's invitation to go bungee jumping."