It's realistic in the sense that it could happen in a normal game without funny moves. The probability is not very high though. Some people may have access to game archives and search tools for such properties but I don't so I can't tell you if it actually happened. Note that it could also happen with more material on the board which is exchanged later leaving the 3 vs 1 bare knights.
3 Knights vs 1 Knight Endgame
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Here is a REALISTIC Endgame where the best move is to
have a 3 knights vs 1 knight endgame; the 3 knights can force
mate. If white promotes to any other piece besides the knight, he will
get forked, resulting in the 2 knights draw. If white doesn't promote
the pawn, it will be taken by the nc5.