https://youtube.com/shorts/_VAz0L0OCHQ
It's a legal move called en passant.
https://support.chess.com/article/683-what-is-en-passant
If it's pawns, that's a pretty normal move although you will rarely see them in practice (maybe 1 in every 50 games at your level)
If it's other pieces, however, then there is cause for concern.
https://youtube.com/shorts/_VAz0L0OCHQ