James, also a baseball historian, took to Twitter on Wednesday to take issue with agent Scott Boras' criticism of teams unwilling to spend in free agency, according to Bill Baer of NBC Sports.
"Because, of course, some players getting more money than they are worth doesn't have ANYTHING to do with it," he said in a since-deleted tweet.
"If the players all retired tomorrow, we would replace them, the game would go on; in three years, it would make no difference whatsoever. The players are NOT the game, any more than the beer vendors are," James said in another tweet that has been removed, per Baer.
Clark, and the MLBPA, responded Thursday morning.
"The comments Bill James made yesterday are both reckless and insulting considering our game's history regarding the use of replacement players," Clark wrote in a statement. "The players ARE the game. And our fans have an opportunity to enjoy the most talented baseball players in the world every season. If these sentiments resonate beyond this one individual, then any challenges that lie ahead will be more difficult to overcome than initially anticipated."
The Red Sox also issued a statement Thursday, distancing the team from James' words.
"Bill James is a consultant to the Red Sox. He is not an employee, nor does he speak for the club. His comments on Twitter were inappropriate and do not reflect the opinions of the Red Sox front office or its ownership group. Our championships would not have been possible without our incredibly talented players - they are the backbone of our franchise and our industry. To insinuate otherwise is absurd."