An infielder is a baseball player stationed at one of four defensive "infield" positions on the baseball field.

In a game of baseball, two teams of nine players take turns playing offensive and defensive roles. Although there are many rules to baseball, in general the team playing offense tries to score runs by batting balls into the field that enable runners to make a complete circuit of the four bases. The team playing in the field tries to prevent runs by catching the ball before it hits the ground, by tagging runners with the ball while they are not touching a base, or by throwing the ball to first base before the batter who hit the ball can run from home plate to first base.

There are nine defensive positions on a baseball field. The part of the baseball field closest to the batter (shown in the diagram as light brown) is known as the "infield" (as opposed to the "outfield", the part of the field furthest from the batter, shown in the diagram as green.)

The infield is composed of four positions: first base (1B), second base (2B), third base (3B) and shortstop (SS). Generally, the first three have responsibility for plays at their respective bases, although the shortstop often shares responsibility for second base with the second baseman. Each position requires a different set of skills. A player who lacks the offensive or defensive skills needed to be a member of the starting lineup, but who has the various skills needed to play two or more infield positions competently and therefore can be called upon to come off the bench and fill a variety of defensive roles is called a utility infielder.

Munenori Kawasaki (川﨑 宗則, Kawasaki Munenori^?, born June 3, 1981 in Aira, Kagoshima, Japan) is a Japanese shortstop for the Seattle Mariners of Major League Baseball. Previously, he played for the Fukuoka SoftBank Hawks of Nippon Professional Baseball. He played for the Japanese national team in the 2008 Beijing Olympics as well as the 2006 and 2009 World Baseball Classics.

Kawasaki was born in Aira, a town in central Kagoshima Prefecture in the south of Japan. He began playing baseball after his older brother got him into the sport. Though he was a pitcher throughout his early years, Kawasaki switched to shortstop after enrolling in Kagoshima Prefectural Technical High School.

Kawasaki remained largely an unknown on the national level during his high school career, partly due to his team's failing to make any national tournaments in those three years. Still, he made a name for himself locally, earning the nickname Satsurō, a portmanteau derived from Satsuma (the name given to a former province of Japan in present-day western Kagoshima) and current Seattle Mariners outfielder Ichiro Suzuki's first name for the similarities in their playing styles. He was drafted in the fourth round of the 1999 NPB amateur draft by the then-Fukuoka Daiei Hawks.