From BR Bullpen
A pinch runner is a substitute used for a runner who is already on base. A pinch runner can be used at any base, and in certain situations, can even enter a game between bases when a player who is entitled to advance to a base without ability to be put out is unable to proceed to that base because of injury (rule 5.10(c)(1)).
When a pinch runner is used, the player for whom he runs is out of the game definitely. The following half inning, the pinch runner may replace the player he substituted on defense as well, or move to another defensive position, or be replaced in turn by a defensive substitute. The only exception is when a pinch runner is used for a designated hitter, he immediately becomes the new designated hitter and is subject to the limitations placed on that position as a result of rule 6.10.
 Courtesy Runners
In the early days of baseball, when rosters were much more limited, there were courtesy runners in addition to pinch runners. A courtesy runner was put in when the normal runner was temporarily incapacitated by an injury. A courtesy runner had to be agreed by the opposite manager, and his presence in the game was not considered as an official substitution. He could therefore be used again once his running duty was completed, or could be a player already in the line-up, and the player for whom he ran would usually return to the game in the next half-inning. In contrast with pinch runners, courtesy runners tended to be slow base runners. The last courtesy runner in a Major League Game was used in 1949 (list of all courtesy runners from Retrosheet) .
 Historical Notes
In contrast with pinch hitters, there are few statistics kept for pinch runners. The job has usually been considered among the most unglamorous in baseball, and except in pennant races when rosters are expanded, it is very rare that teams will carry a pinch running specialist on their roster.
One exception to this rule is the Oakland Athletics of the early 1970's. Team owner Charles Finley was convinced that speed was an essential element of a winning ball club, and that having a specialist pinch runner on hand would give his team five to ten additional wins every year. He therefore made sure that such a specialist was on the roster. At first, he used speedy outfielder Allan Lewis (known as The Panamanian Express) in this role, from 1967 to 1973, then in 1974, he hired a track star with no baseball experience, Herb Washington, for the role. Washington was used in 91 games that year, scoring 29 runs and stealing 28 bases without a single plate appearance or game in the field. However, his instincts as a ball player were poor, and in 1975, he was released after a few games while former minor league outfielder Don Hopkins took over for him, being used in 82 games, while picking up 8 plate appearances and playing five games in the outfield. After a few games in 1976, Hopkins made way for Larry Lintz, who had been a semi-regular for the 1974 Expos. Lintz had three plate appearances that season in 68 games, but stole 31 bases. He continued in the same role in 1977, but was also used as a back-up infielder, getting almost 40 plate appearances in addition to his pinch running duties.
No other team has tried to carry a full-time pinch runner on its roster since that experiment, although a few other major league players have made their only appearances in a game as a pinch runner, notably Mel Kerr for the 1925 Cubs and Gary Hargis for the 1979 Pirates. Other teams have occasionally kept pinch-running specialists for brief stretches, such as Matt Alexander, but with expanded pitching staffs such a luxury has not been available in recent years. Japanese teams, with larger rosters, still sometimes carry pinch-running specialists.
 Further Reading
- Clifford Blau: "Leg Men: Career Pinch-Runners in Major League Baseball", in The Baseball Research Journal, SABR, Volume 38, Number 1 (Summer 2009), pp. 70-81.
- Scott Schleifstein: "Herb Washington's Value to the 1974 A's", in The Baseball Research Journal, SABR, Volume 38, Number 1 (Summer 2009), pp. 82-87.