Jonathan Papelbon. (Alex Brandon/AP)

In an effort to overhaul their bullpen, the Nationals have been strongly pursuing free agent reliever Darren O’Day, according to reports. The side-arm, submariner right-hander has been one of the best relievers in baseball over the past several years. His ERA has dropped from 2.28 to 2.18 to 1.70 to 1.52 over four seasons. He has averaged 66 innings and posted no more than a 1.000 WHIP (walks and hits per inning pitched) each of the past four seasons for the Orioles.

His fastball is in the mid to high 80s, but he thrives on his unusual arm angle, deception and movement. In his all-star 2015 season, he also saved six games. The 33-year-old was effective against batters from either side of the plate: he held right-handers to a .192 average and left-handers to a .210 average. His strikeout rate in the past four years is nearly 10 per nine innings.

In a weak free agent relief market, O’Day is the top choice and, as a result, pricey. According to Fox Sports, O’Day agents are seeking a four-year deal in the range of $28-36 million. The Nationals have been reluctant to spend big money on free agent relievers in the past because the position is so volatile and putting dollars there can be inefficient. The largest deal they’ve given a free agent reliever was Rafael Soriano’s two-year, $28-million deal. The Nationals, however, have little choice and need to improve the bullpen and add experienced arms.

According to an ESPN report, the Dodgers and Nationals are pursuing O’Day the most. O’Day’s family lives in Atlanta, and the Braves have been pursuing him, according to a CBS Sports report. But O’Day’s wife, Elizabeth Prann, is a Fox News reporter based out of Washington.

As the Nationals sort out their bullpen, they have many moving parts. General Manager Mike Rizzo has made clear publicly that he won’t trade Jonathan Papelbon or Drew Storen unless he receives a good offer, but that simply could be his way of trying to preserve value. Privately, many believe the Nationals will attempt to trade either or both. The relationship between the team and both relievers has frayed some, including with Papelbon, who was in a fight with Bryce Harper at the end of the season and was suspended four games without pay.

Here’s a wrinkle to the situation: Storen is a year away from free agency and can be traded anywhere, while Papelbon still has a partial no-trade clause for 2016 and he recently updated the list of teams he can be traded to. Before his trade to the Nationals in July, Papelbon had to approve it because Washington was on the list of teams that required his consent. Last winter, Papelbon chose 12 he would accept a trade to, meaning he could block a trade to the other 17.

Papelbon has the right to update the list yearly and he did so for 2016, according to someone familiar with the situation. But if there was a trade lined up, Papelbon isn’t expected to be an issue. Trading him to another team will be a challenge given his past behavior and $11 million salary in 2016.