He's too agitated to calm down (6)
I believe the answer is:
soothe
'calm down' is the definition.
(I've seen this before)
'he's too agitated' is the wordplay.
'agitated' is an anagram indicator.
'hes'+'too'='hestoo'
'hestoo' anagrammed gives 'SOOTHE'.
'to' is the link.
(Other definitions for soothe that I've seen before include "Console, pacify" , "to settle" , "Cause to feel better" , "Gently calm" , "Calm down, placate" .)