Senior England sides chasing silver (4)
I believe the answer is:
aged
'senior' is the definition.
(synonyms)
'england sides chasing silver' is the wordplay.
'sides' suggests removing the centre (only the letters on the sides are used).
'chasing' is a charade indicator (letters next to each other) (some letters chase after others).
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'england' with its middle taken out is 'ed'.
'ed' put after 'ag' is 'AGED'.
(Other definitions for aged that I've seen before include "Mature" , "Advanced in years" , "Very old, person or wine" , "Antiquated" , "Matured like wine in wood" .)