What Is a Fifth Infielder in Baseball?

A fifth infielder is an outfielder who moves into the infield, so the defense plays five infielders and two outfielders. Teams use it in one situation above all: the winning run is on third base, there are fewer than two outs, and it's the last inning or extra innings.

Why it makes sense

With the winning run on third and less than two outs:

• A fly ball to the outfield deep enough to be caught will usually score the run on a sacrifice fly, so outfielders can't do much.
• A ground ball through the infield ends the game.
• A ground ball at an infielder gives the defense a chance to throw home or turn a double play.

So the defense gives up outfield coverage it can't use anyway and puts another glove where the game-winning grounder is likely to go.

How it's set up

• Usually the left or center fielder moves in, often playing near second base or between the pitcher and first base.
• The corner infielders usually play in on the grass to cut off the run at the plate.
• The two remaining outfielders split the outfield, often shallow.

The exact positions depend on the hitter. Against a pull hitter, the extra infielder goes to that side.

Is it legal under the shift rules?

Yes. MLB's 2023 rules require at least four players on the infield dirt when the pitch is thrown, two on each side of second base. They don't stop a team from bringing an outfielder in, so a five-man infield is still allowed.

Does it work?

It's a gamble. If the batter hits a fly ball or a looping line drive over the drawn-in infield, the game is over either way. But managers use it because it raises the odds of the one play that can save the game: a ground ball hit at someone. Even when it fails, it usually fails in a way that would have ended the game anyway.

Related terms

• Utility player: the versatile fielders who often fill this role
• Walk-off: what the offense is trying to do
• Types of outs: force outs, tag outs and double plays

More definitions: baseball terms explained.

Frequently asked questions

What is a fifth infielder?

It is a defensive alignment where an outfielder moves into the infield, giving the defense five infielders and two outfielders. It is used to cut off ground balls when one run will decide the game.

When do teams use a five-man infield?

Most often in the bottom of the ninth or extra innings, with the winning run on third base and fewer than two outs.

Is a fifth infielder legal under the shift rules?

Yes. Since 2023 MLB requires at least four infielders on the infield dirt, two on each side of second base. Adding an outfielder to the infield is still allowed.

Why not keep the outfielders back?

With the winning run on third and less than two outs, a fly ball deep enough to catch usually scores the run anyway on a sacrifice fly. A ground ball is the only realistic chance to get the runner.