A combination is usually built out of more fundamental chess tactics such as forks, pins, skewers, undermining, discovered attacks, etc. Thus a combination must be at least three moves long, but the longer it takes to recoup the initial sacrifice, the more impressive the combination. The position below begins a combination which illustrates several forks and skewers. Black played 1... Rxf3+! White dare not take the rook with 2.Kxf3 because of the royal fork 2... Nd4+, which would win the white queen. Retreating with 2.Ke2 instead would run into the same fork. The move 2.Kd2 looks more promising, but after 2...Rf2+ (skewering the white king and queen) 3.Be2 Rxe2+ 4.Kxe2 Nd4+ the white queen will be lost anyway. Therefore White was forced to play 2.Ke4.
After 2...d5+!, White resigned. White still could not take the black rook without losing his queen, but the alternative 3.cxd5 exd5+ 4. Kxd5 Be6+ would leave White with no good defense. Taking the bishop with 5.Kxe6 allows the long-threatened fork 5...Nd4+, while taking the knight with 5.Kxc6 allows the skewer 5...Rc8+ followed by 6...Rxc2. Retreating with 5.Ke4 permits the black bishop to skewer the white king and queen with 5...Bf5+, so White has only one option left: 5.Kd6.
After 5.Kd6, Black would have played 5... Rd8+. White couldn't take the bishop or the knight for exactly the same reasons as before (after 6.Kxe6 Nd4+ 7. Ke7, Black comes out a rook ahead with 7... Nxc2 8.Kxd8 Nxa1), which leaves one legal move, namely 6.Kc7, but then 6... Rf7+ absolutely forces the white king to take the black knight, allowing the skewer 7... Rc8+ followed by 8...Rxc2.