Rare term for an arrow that misses its target and flies off course; synonymous with the more common 流れ矢 (ながれや).
See also: 流れ矢
古戦場では狐矢に当たる危険があった。
On ancient battlefields, there was a danger of being hit by stray arrows.
The origin of the reading きつねや is uncertain; the kanji 狐 (fox) and 矢 (arrow) may be ateji or a folk-etymological association.