noun
simultaneous strike; mutual hit
Primarily used in kendo and similar martial arts for when both opponents strike each other at the same time. Also used metaphorically for any simultaneous action or clash.
試合は相打ちとなり、両者に一本が与えられた。
The match ended in a simultaneous strike, and both were awarded a point.
議論は相打ちに終わり、結論は出なかった。
The debate ended in a draw, and no conclusion was reached.
Compound of 相 (ai, 'mutual') + 打ち (uchi, 'striking'), the nominalized form of 打つ (utsu, 'to strike'). The spelling variants 相撃ち and 相討ち use different kanji for 'strike' with similar meanings.