Sets up amount of numerical data about king (6)
I believe the answer is:
starts
'sets up amount of numerical' is the definition.
I can't tell whether this definition defines the answer.
'data about king' is the wordplay.
'data' becomes 'stats' (statistics are a kind of data).
'about' is an insertion indicator.
'king' becomes 'r' (r is abbreviation for rex).
'stats' going around 'r' is 'STARTS'.
Can you help me to learn more?
(Other definitions for starts that I've seen before include "reacts in surprise" , "Reacts in shock" , "origins?" , "breaks" , "Makes sudden movement from pain or surprise" .)