Error; false move (7)
I believe the answer is:
misstep
I believe this is a double definition.
'error' is the first definition.
(misstep can mean an error or mistake)
'false move' is the second definition.
(I've seen this before)
(Other definitions for misstep that I've seen before include "Badly judged move" , "bad move" , "Badly judged footing" , "Error" , "False move" .)