NEW YORK — Players’ union head Tony Clark took the extraordinary step of saying baseball fans should question whether it makes sense to purchase tickets for some teams, responding to Commissioner Rob Manfred’s assertion that free-agent players have failed to adjust their economic demands in a market upended by analytics.

Top free agents Bryce Harper, Manny Machado, Craig Kimbrel and Dallas Keuchel remain unsigned with spring training underway, creating tension during negotiations on management’s proposals for a pitch clock.