Possible Clues:

• Sport with the biggest cast of all!
• What a fishy way to be getting one's degree, perhaps
• Walton practised it, seeking compliments, perhaps?
• A 'no good' fish? Not what's wanted in this sport
• Indirectly seeking riverside activity?
• Don't start -- suspended for fishing!
• No good spearing a fish — try this instead?
• Getting involved, with no time for water sport
• Fishing with a hook and line
• Activity by the banks that may bring no gain!