Sometimes a piece can be attacked and protected multiple times. A sequence of captures can then happen on that square, as in the following examples:

In the first diagram, White’s bishop and rook are attacking the knight, which is only protected by the rook. White can capture the knight with either bishop or rook to win material. If Black recaptures with the rook, White will still have one attacker left and can recapture again. Such a sequence of captures and recaptures on the same square is called a trade. In any given position, it is always important to look at the possible trades and determine their outcome. They can win material, lose material, or exchange equal amounts of material.

In the first diagram, bishop and rook are attacking from different directions, but a trade is also possible with two or more pieces attacking from the same direction, as in the second diagram: White can capture the knight with the first rook to win material. If Black recaptures with the rook, White can recapture again with the second rook, because the first rook will be out of the way.

Rooks, queens, and bishops are long-range pieces, which means they can attack pieces that are far away. With this long-range ability, the second rook in the diagram is attacking Black’s knight “through” the first rook. Such a powerful formation of two or more long-range pieces operating in the same direction is called a battery.

A battery is also possible on a diagonal, as in the third diagram. White can capture the knight with the bishop. If Black recaptures with the rook, White can recapture again with the queen, because the bishop will no longer be in the way of the queen.

Examples

Black can use the battery on the d-file to win a rook by trading on d2: 1...Qxd2 2.Qxd2 Rxd2
The Rook on d2 is insufficiently protected.

Sometimes there are multiple possible captures on the same move. In most of these cases, it is sufficient to calculate the trade with the least-valuable piece capturing first.

White is attacking the bishop on d7 with the queen and the bishop on f5. White has a winning trade, but has to capture with the bishop first: 1.Bxd7 Nxd7 Qxd7+. Capturing with the queen first would not be a good idea: 1.Qxd7? Nxd7 2.Nxd7 and White would have lost a queen for bishop and knight, a material equivalent of losing three pawns.

How to spot a winning trade

After each capture, calculate the sequence of trades on that square.

Remember that you are not forced to make any subsequent captures. If the subsequent capture would not gain further material, it might be better to stop trading and play a different move (especially if subsequent trades would lose material).

With some practice you will be able to spot winning trades very quickly and analyze more complicated trades with confidence. Captures and trading are the fundamental ways to win material and are the basis for learning more advanced tactics.