Get Castro in a tizzy introducing American items of clothing (10)

'items of clothing' is the definition.
(greatcoat is a type of garment)

'get castro in a tizzy introducing american' is the wordplay.
'in a tizzy' indicates anagramming the letters (being in a tizzy is being confused).
'introducing' is an insertion indicator (some letters introduced or inserted into others).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'get'+'castro'='getcastro'
'getcastro' anagrammed gives 'greatcots'.
'greatcots' placed around 'a' is 'GREATCOATS'.