Chap has mistakenly begun to restrict pulse (4,4)
I believe the answer is:
mung bean
'pulse' is the definition.
(I know that mung bean is a pulse)
'chap has mistakenly begun' is the wordplay.
'chap' becomes 'man' (chap can mean a man).
'has' indicates putting letters inside.
'mistakenly' indicates an anagram.
'begun' with letters rearranged gives 'ungbe'.
'man' placed around 'ungbe' is 'MUNG BEAN'.
'to restrict' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for mung bean that I've seen before include "Edible seed" , "Tropical vegetable" .)