[blue hen house]

As I stepped through the gate to the lawn ( what there is left of one ) Stella
(light sussex x) slipped passed me looked at Bilbo( choc lab dog) and flew
straight at his open mouth.The dog tried to bark, but just got a mouthfull
of Stellas' bum feathers. My husband told Bilbo to sit which he did after spitting out the feathers and Stella was ushered back through the gate.
She stood the other side of the gate looking at Bilbo with a "Yea you want it dog, bring it on!. Chooks never know whats next  

[Aunt Sally]

Chickens can be feisty creatures.  

[Fat Hen]

Our chucks jump over our old German Sheperd (the younger one keeps out of the way) thats usually layed across the open patio door.  To get in house and watch telly etc.  Maybe your chuck was actually trying to vault the dog and misjudged