An extra-base hit is defined as any hit that is not a single, meaning doubles, triples and home runs are all considered extra-base hits. They are a good stat to look at to evaluate an offensive player's power -- and in some cases, his speed.
An extra-base hit is typically a ball that is hit very hard, and it often goes to the outfield wall. (Obviously, in the case of a home run, it usually goes over the wall). Speedier hitters have a slight advantage in attaining extra-base hits because they can use their foot speed to reach second base faster.
Extra-base-hit totals can also be used to evaluate pitchers, although this is done less frequently. In that case, it is referred to as extra-base hits against.
Watch: Ryan Zimmerman collects an extra-base hit with a double.
In A Call
"extra bags," "long hit"