An at bat in which the batter is productive in a way that fits the situation, whether that involves advancing the runner with a sacrifice bunt or even a ground ball out, getting on base, or making the pitcher throw a lot of pitches. Thus a quality at bat is not measured simply by the standard batting statistics such as batting average, on-base percentage, or slugging average. Minnesota Twins catcher Joe Mauer: "Seeing a lot of pitches, fighting bad pitches off – basically, just waiting for a pitch you can handle. Whether you’re a power guy, or more of a slap hitter guy, if you find a pitch you’re comfortable in handling, that’s a quality at-bat. If you get on base or drive a ball up the gap, you pretty much know you had a good plate appearance. But it’s mostly about making sure you get your pitch."
When a starter pitches at least 6 complete innings and allows 3 or fewer earned runs -- even in a loss. A pitcher can perform well yet not be involved in the win-loss "decision". This statistic was developed by sportswriter John Lowe to capture an aspect of pitcher performance that is not part of the standard statistics collected by Major League Baseball. It is catching on among baseball players and management, but also has some skeptics. Former Houston Astros manager Jimy Williams was said to hate this statistic. "Quality start?" he would harumph. "Quality means you win."
An illegal pitch where the ball thrown is before the batter is set in the batter's box. (Official Rules of Baseball, Rule 8.05(e)) If there is no one on base, the pitch is called a ball, but if there are any number of runners on base, it is ruled a balk. The ruling of a quick pitch is always up to the umpire.
When a pitcher prevents the opposing hitters from getting a lot of hits, or big hits, he's said to have "quieted some bats". "Iowa's starting pitcher, Jarred Hippen was able to quiet the Spartans' bats the rest of the way to seal the victory". Headline: "Miscues, Quiet Bats, Cost D-Backs".
A batter who holds his head, hands, and bat very still while awaiting the pitch may be said to have a quiet swing. "Hideki Matsui's quiet swing and stance are a big part of the reason why he is able to hit for both power and average.
Glossary of baseball (Q) Wikipedia