Harrison's fine was announced a few hours after the league said it would immediately begin suspending players for dangerous and flagrant hits, particularly those involving helmets.
Although Harrison wasn't suspended, his agent, Bill Parise, called the fine "staggering" and said he would appeal.
"I've talked to James, and he's very upset," Parise said. "He's quite confused about how to play football."
Earlier, Harrison said it would be a "travesty" if the league took action against him.
Harrison, the 2008 Associated Press NFL Defensive Player of the Year and a three-time Pro Bowl outside linebacker, rammed headfirst into Massaquoi as the receiver attempted to complete a catch during the second quarter. Massaquoi briefly crumpled to the turf but was soon on his feet, although he didn't return to the game.
That play occurred a few minutes after Harrison's helmet-first hit sidelined Browns wide receiver Joshua Cribbs with a concussion. Harrison lowered his head and drove into the left side of Cribbs' helmet, a tackle the NFL said Monday was permissible because the receiver was a runner on the play. That hit didn't factor into Harrison's fine, and the linebacker wasn't penalized on either play.
Tomlin called both tackles "legal hits, not fineable hits," but the league didn't agree with him on Harrison's hit on Massaquoi.
Harrison not only wasn't apologetic for the hits, he said he tries to hurt players because it increases the Steelers' chances of winning. Harrison drew a line between hurting and injuring, saying his intent wasn't to put players out of games.
With Cribbs unable to run the Wildcat formation that Cleveland used effectively in upsetting Pittsburgh, 13-6, in December, the Steelers went on to a 28-10 victory Sunday.
"I didn't see those comments, but I know James," Tomlin said. "James says a lot of things he doesn't necessarily mean. He's a tough talker, like a lot of guys that play the game at this level. If you want to get to know James, catch him on a Tuesday when he's walking through the building with his son. He's a big softie."
Tomlin argued there is room in the league for physical play like the Steelers encourage, yet also safe play. One way to eliminate some helmet hits, he said, is to further emphasize a lowering of the strike zone, the area where players are tackled.
"I'm all for player safety. I think it is the proper initiative that the NFL has," Tomlin said. "I think we need to safeguard the men that play this game to the best of our abilities and make it as safe as we can. I'm a proponent of player safety and whatever rule or rule adjustments we need to make to make it safer."
Copyright 2010 by The Associated Press