A Fly Ball is Dropped

For a ball hit into the outfield to go for an error, it basically means that a fielder is going to have to get a glove on it, but not haul in the catch. There are a few ways this can happen— feast your eyes, if you dare— but the end result is the same: an error, which ends up extending the inning for your pitcher, and that can have… disastrous consequences.

Unless there were already two outs before the ball was hit, the baserunners will likely linger around their bases until they see the ball drop in¹. Once that happens, they're off and running; if the defense can recover the ball quickly enough, they might be able to make a play on one of those runners. Once everything dies down, the inning continues.