Obtained legal document to restrict half the competitors (7)
I believe the answer is:
derived
'obtained' is the definition.
(deriving is a kind of obtaining)
'legal document to restrict half the competitors' is the wordplay.
'legal document' becomes 'deed' (deed is a kind of legal document).
'to restrict' is an insertion indicator.
'half' means to take half the letters.
'the competitors' becomes 'rivals' ('rival' can be a synonym of 'competitor').
'rivals' with half the letters taken is 'riv'.
'deed' going around 'riv' is 'DERIVED'.
(Other definitions for derived that I've seen before include "Inferred" , "Formed or developed from something else" , "Traced the source" , "Procured" , "Obtained/drawn (from)" .)