Description of movement's frequently a mess if Spooner spits it out (4-13)
I believe the answer is:
post-impressionist
'description of movement's' is the definition.
(description of an art movement)
'frequently a mess if spooner spits it out' is the wordplay.
'frequently' means one should take alternating letters (letters selected at a regular frequency).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'mess'+'if'='messif'
The alternating letters of 'messif' are 'msi'.
'msi'+'spooner'+'spits'+'it'='msispoonerspitsit'
'msispoonerspitsit' with letters rearranged gives 'POST-IMPRESSIONIST'.
(Other definitions for post-impressionist that I've seen before include "Cezanne or Gauguin, perhaps" , "Artist such as Gauguin or Seurat" , "Artist in a particular style" .)