If a creature had to make both saving throws for ball bearings and caltrops, and failed the ball bearings - Would they automatically fall prone & land on the caltrops, taking caltrop damage with no chance for a caltrops saving throw (or regardless of a passed caltrops saving throw)?
Inspired by this answer to this question If an area is covered in both Ball Bearings and Caltrops, does the creature need to move at half speed or quarter speed to avoid both their effects? where it's mentioned:
Note that if the creature chose to move greater than half their speed across the combined area then they would be forced to make both saving throws, one against the ball bearings and one against the caltrops, possibly suffering one effect or the other effect or both effects combined.