Most enthusiastic in study, enthralled by craft (6)
I believe the answer is:
ardent
'most enthusiastic' is the definition.
'study enthralled by craft' is the wordplay.
'study' becomes 'den' (I've seen this before).
'enthralled by' indicates putting letters inside ('enthral' can mean 'capture').
'craft' becomes 'art' (I've seen this before).
'den' put into 'art' is 'ARDENT'.
'in' is the link.
(Other definitions for ardent that I've seen before include "full of zeal" , "Burning, passionate" , "Burning with emotion" , "passion" , "'Fervent, impassioned (6)'" .)