to knock together; to strike against each other
to arrange (e.g. a meeting); to discuss (in advance)
剣士たちは竹刀を打ち合わせた。
The kendo students clashed their bamboo swords.
騎士たちは剣を打ち合わせて激しく戦った。
The knights clashed their swords and fought fiercely.
グラスを打ち合わせるのが乾杯の習慣だ。
It is customary to knock glasses together when toasting.