Possible Clues:

• They're all round but only half round, of course (4, 5)
• Only half 5 down, yet that's the drill for them, of course
• After half a round one might drill them all
• Half of a course
• A quick round of golf
• Drilled only half round
• They're drilled only half way round, of course
• They're all dug half round, of course
• They're all round, but of course they're only half round
• They're all-rounders; together, they're half round, of course