In double-play situations, shortstops will often protect the second base bag on grounders hit back to the pitcher. A competent defensive shortstop must have exceptional range, a strong throwing arm, and the ability to cleanly field hit balls. Although they generally do not get the attention of other players on the field, shortstops are among the most important positions because of their impact on double plays and potential game-ending errors. The modern shortstop covers about 275 feet along the basepaths during an average play at home. This is more than any other position except for first base (335 feet) and catcher (315 feet). A common error by shortstops is going too far toward a line drive or fly ball, which increases their risk of being thrown out at first. They should also keep an eye on popups near them in case one is caught off balance or makes a bad throw. At times, two shortstops will be used simultaneously to replace one injured player. This is usually done when one shortstop is unable to handle playing time due to injury or poor performance. Sometimes, two middle infielders are used instead, depending on the manager's strategy. Using multiple shortstops at once is most common with younger teams that may not have enough major league talent to properly fill out their roster.