An overhead span, I see, heard to be in disorder (8)
I believe the answer is:
anarchic
'disorder' is the definition.
(I've seen this before)
'an overhead span i see heard' is the wordplay.
'an overhead span' becomes 'anarch' (I can't explain this - if you can you should believe this answer much more).
'heard' indicates a 'sounds like' (homophone) clue.
'see' is a homophone of 'c'.
'anarch'+'i'+'c'='ANARCHIC'
'to be in' is the link.
Can you help me to learn more?
(Other definitions for anarchic that I've seen before include "Totally uncontrolled" , "Uncontrolled or lawless" , "rioting" , "Lawless, out of control behaviour" , "Without law or control" .)