Possible Clues:

• Thrashed (about)
• Swung wildly
• Danced ungracefully
• Didn't manage to cross line, so beaten
• Thrashed around
• Made things harder for the lifeguard
• Threshed grain
• Swung wildly and did not manage to hold line
• Thrashed around, having failed to get in first lifeboat
• Complicated a lifeguard's rescue