Perfect for example holding a lead, become nervous (5,2)
I believe the answer is:
tense up
'a lead become nervous' is the definition.
I can't tell whether this definition defines the answer.
'perfect for example holding' is the wordplay.
'perfect for example' becomes 'tense' (perfect is a kind of tense).
'holding' becomes 'up' (I can't explain this - if you can you should give a lot more credence to this answer).
'tense'+'up'='TENSE UP'
Can you help me to learn more?
(Other definitions for tense up that I've seen before include "become edgy" , "become uneasy" , "Become stiff through stress or anxiety" .)