During ESPN's NBA Countdown on Friday, Pierce said (starting at 5:55 mark): "Players of today are scared of LeBron. ... My era is out the league. We wasn't afraid of LeBron, but these guys today, he strikes fear in these guys. I can see it."
In 14 seasons that their careers overlapped, James averaged 27.1 points, 7.3 rebounds and 7.0 assists per game. He won four MVP awards and three championships and was named to the All-NBA first or second team 13 times.
Pierce has a well-documented history of criticizing James. Kendrick Perkins said on ESPN's Hoop Streams in May that the feud began when Pierce spat at the Cleveland Cavaliers bench in a preseason game during Perkins' and James' rookie season, 2003-04.
"Paul is talking noise to the bench, right?" Perkins said (h/t Zac Al-Khateeb of Sporting News). "He's talking big noise to the Cavs bench, and they're sitting over there, Bron and them, they're all sitting over there. ... Paul actually spits over there at the bench, right? The ultimate disrespect."
Pierce had dissed James by leaving him out of his top five players of all time, saying he didn't "build up" his organizations.
In James' 11 seasons with the Cavs, they made the playoffs nine times, including five Finals appearances, and won the 2015-16 championship. They have just 13 postseason appearances and four series wins in 39 seasons without him.
En route to winning his first title during the 2011-12 season, James led the Miami Heat to a victory over Pierce and the Boston Celtics in a seven-game Eastern Conference Finals.