Such a big basket could slow you down (6)
I believe the answer is:
hamper
This could be a double definition.
'such a big basket' is the first definition.
(I've seen this before)
'slow you down' is the second definition.
'hamper' can be an answer for 'slow' (thesaurus). I am not certain of the 'you down' bit.
'could' is the link.
Can you help me to learn more?
(Other definitions for hamper that I've seen before include "Slow up - basket" , "Large covered basket" , "Restrict, hinder" , "Hold up in a basket?" , "Christmas basket" .)