So I see you've given in!
Here are some hints:

Can't beat those pesky crabs huh? Have you been reading Asakawa's instructions!? I doubt it.
No worries. I'll stop shaming you! You've come to the right place to get all the answers.
Step 1: Don't just choose fight!
Step 2: Choose Item
Step 3: Choose the Net
Step 4: If the word "CAUGHT!" appears on the screen, you've got the crab! congratulations. goto step 5.
Otherwise goto step 1.
Step 5: Choose the club. Continue step 5 until you win.
And there you have it! That's how you beat those pesky crabs.