To make it clear, I want to stick to known physics. Otherwise, the most creative tactic is "hypometric weapons" from Reynold's Absolution Gap -- your enemies (or parts of your enemies, if you are feeling "creative") simply disappear. Indistinguishable from magic. And when Inhibitors adapted, hypometric weapons "simply stopped working against them". Bigger magic.

Although Absolution Gap had some creative tactics within realm of possible. Such as what happens when two relativistic starships are travelling from one star to another at same speed, one few light-hours ahead of the other? Keep in mind that "throw ball bearings in the path of pursuer" is not particularly effective because ball bearings will retain velocity and just keep on alongside the lead ship. Anything you care to throw from either ship to the other must be accelerated, and thus can not be completely invisible.

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Fiction has to be plausible. Reality is under no such constraint.