Calzaghe and Froch never actually fought each other. Their careers overlapped briefly when Froch was just starting out and Calzaghe was already a big name in boxing.
Calzaghe, from Wales, was a world champion at super-middleweight before moving up to light heavyweight and winning there too. He beat some big names like Chris Eubank Sr, Mikkel Kessler, Jeff Lacy, Bernard Hopkins, and Roy Jones Jr. Calzaghe retired undefeated after 46 fights.
Froch also did well in the super-middleweight division. He only lost to Andre Ward and Mikkel Kessler, but he got back at Kessler in a rematch. Froch's big wins included Jean Pascal, Lucien Bute, and George Groves in his last fight in 2014.
In an interview with Sky Sports, Ward said he thinks Calzaghe would win on points if they had fought. He explained:
"I don't think Froch could have kept up with the pace. Calzaghe had good footwork. That's kryptonite to Carl Froch, he doesn't have great feet at all. I'm not going to say Calzaghe would have blown Froch out, cause Froch had the desire, the unwillingness to give up, we saw that with Jermaine Taylor when he kept coming and eventually knocked the door down."
Ward thinks Calzaghe's quick feet and high punch count would've been too much for Froch. But he also gives credit to Froch for being tough and never giving up. Ward believes the fight would've been competitive.
Frank Warren, who used to promote Calzaghe, agrees with Ward. He still says Calzaghe would've won if they had fought.