to come down heavy on

米大リーグ機構が薬物問題に厳しい姿勢を示したのはご存知の通り。薬物規定違反による１３選手への出場停止処分を発表し、ヤンキースのアレックス・ロドリゲス内野手には、今季残りと来季全試合の計２１１試合の出場停止処分という厳罰を下しました。

MLB suspends 13, including A-Rod

Major League Baseball came down heavy Monday on the players it found to have been involved with the South Florida anti-aging clinic Biogenesis, suspending Alex Rodriguez through the end of the 2014 season and banning 12 others for 50 games, including three All-Stars: Nelson Cruz of the Texas Rangers, Everth Cabrera of the San Diego Padres and Jhonny Peralta of the Detroit Tigers.

"Obviously, I'm disappointed with the news today," Rodriguez said at a news conference before Monday's game. "What we've always fought for is the process and I think we have that, and I think at some point we'll sit in front of an arbiter and we'll give our case. That's as much as I feel comfortable saying right now."
He called the past seven months a "nightmare."
"Probably the worst time of my life for sure," he said. "Obviously, for the circumstances that are at hand, and dealing with a tough surgery and a rehab program and being 38."
"I am thrilled and humbled to have the opportunity to put on this uniform again and to play major league baseball again," he continued. "I feel like I was 18 years old back in Fenway Park in 1994 when I went in to face the Red Sox for the very first time. It's been 20 years ... very excited to get out there to play baseball and to help my team win and to prove to myself, my teammates, the fans of New York, the fans of baseball, that I still have a shot to play the game at a high level and I'm going to give it my best."

Asked if he denies using performance-enhancing drugs, he said: "We'll have a forum to discuss all of that and we'll talk about it then."

http://espn.go.com/mlb/story/_/id/9540755/mlb-bans-13-including-alex-rodriguez-new-york-yankees-2014

最初の文にあるcome downは「決定する、決める」というおなじみのフレーズですが、ここではheavyを伴って「重い決定を下す」という意味。onはその対象を示しています。
面白いのは、これにはcomedownという名詞をほうふつさせるように仕掛けがあることです。ネイティブであればこのPVから派生したcomedown（期待はずれ、おちぶれたもの）を想起し、さらにはその俗語である「麻薬、薬物」という俗語も連想するでしょう。ESPNもやりますね。（UG）