A Ball Mark Inspection (BMI) is an event that only happens on clay courts.
They work very similarly to challenges, a BMI happens when a line judge calls a ball and the team/player disagrees. The umpire will then come down to the court and take a look at the mark that the ball made on the clay, and judge if the ball was out or in.
Packet
A BMI will occur at the same time as a challenge - After 'Point Started' and before the 'Point' packet.
It does not include information on if it was 'won' or 'lost' - just that there was a BMI. The next point is always the outcome of the BMI (who the point is awarded to).