Here's the complete hand:
You must win the 1st trick - for starters. The key word is "unbalanced" which means West has a stiff or void. If its in hearts or clubs, you would have heard something from RHO holding 6 or 7; so trumps are probably 4-1.
After the 10 drops on your right, you can play a club up, and this is what happened at the table. Exit a club, and the J wins on your right. (Note: LHO can win the club, cash the diamond, and give his pard a diamond ruff for -1, but even the great players miss plays like this)
RHO exits a heart. Play A
♥,
♥ to King, ruff
♥, ruff club, ruff heart as RHO follows. The position is now:
South has already made 8 tricks (A
♠, 2
♥, 2
♥ ruffs, A
♦, K
♣ and a
♣ ruff). A diamond exit gets two more.
Its technically better to take the heart ruff first, before leading a club to the King. However, this makes the position more evident to the defense as well. In the actual hand, if the defense forces the board early with a heart, you don't have the entries to ruff the 4th heart.