clubbing baby seals 

When sailors want to kill a baby seal, they have 3 ways to do it. Either shoot it in the head, hit it with a blunt object or a hakapik. They usually go for the hakapik since it's the easiest to use, but if they don't have one, they will use the blunt object (like a baseball bat or golf club). It is also used as a saying because it is an easy task if you hit the seal right in the head, similar to shooting fish in a barrel.

"When I was working on the boat, they made me club baby seals"
"We won the race with 3 minutes to spare. It was like clubbing baby seals."

clubbing baby seals by Skalkin November 10, 2019