Fleetcatch
From Planetarion Wiki
A fleetcatch is a tactic used to varying degrees of success throughout PA history to destroy the ships of a particular planet. An alliance (or other group of players) co-ordinate sending attacking fleets to coincide with the returning of the target planet's fleet, in essence "catching" the returning fleet.
Fleetcatches require precise coordination. It is recommended to launch less than 10 seconds before the tick to make it very hard for the target to detect anything by doing a JGP scan on themselves. For the same reason it's very important that nothing gets leaked.