Chicken, fourteen pounds, seen in US national park (11)
I believe the answer is:
yellowstone
'us national park' is the definition.
(I've seen this before)
'chicken fourteen pounds' is the wordplay.
'chicken' becomes 'yellow' (as in cowardly).
'fourteen pounds' becomes 'stone'.
'yellow'+'stone'='YELLOWSTONE'
'seen in' is the link.
(Other definitions for yellowstone that I've seen before include "Topaz, perhaps" , "First US national park, 1872" , "River with falls in Wyoming" , "US river" .)