Double attack
One move, two threats. The opponent answers one and loses the other. Queens and knights make the cheapest ones.
White to play
Qa4+
The queen checks the king along one line and touches the loose bishop along another. The check has to be answered, so the bishop goes.
What to look for
After any candidate move, list everything the moved piece now attacks. If two of those are worth taking and both are undefended, you have one.
When it applies
Any time the opponent has two loose pieces, or a loose piece and an exposed king. A check plus a threat is the strongest form because the check is not optional.
How it goes wrong
Two attacks on defended pieces is not a double attack — it is two threats they can ignore. The targets have to be genuinely takeable.
Where it came up
Not cited in your current game.
Practise it
No positions yet. When you miss this idea in a game, the position it cost you shows up here — and in the practise set — with the answer hidden.