It might sound crazy to think that the Rockies are sending a bullpen pitcher with a 3.75 ERA down to Triple-A right now. For a club with a 4.32 bullpen ERA and overall team ERA of  5.15, Miguel Castro is on the south side of both of those numbers.

In fact, he’s allowed earned runs in just three of his 13 appearances. Save for a bad day in Cincinnati, he’s never allowed more than one run to cross the plate.

So again, why would the Rockies send him down?

Well, for one, they’re getting a pitcher back in Boone Logan who’s been even better in 2016.

That might come as a surprise to Rockies fans, who recall Logan’s 4.33 ERA in 2015 and 6.84 effort in 2014, but Logan has actually been the club’s most reliable bullpen arm before landing on the 15-day disabled list due to shoulder inflammation.

In 18 appearances – already more than half his 2014 campaign – Logan boasts a team-low 1.93 ERA. He’s allowed three earned runs on nine hits over 14 innings pitched while striking out 17 and walking just five.

Logan was placed on the disabled list May 25, retroactive to May 18, due to left shoulder inflammation (throwing arm). He currently has a scoreless-inning streak of 10.2 innings, the fifth-longest active streak in the National League.

He made one rehab appearance, pitching one scoreless inning Saturday for Albuquerque at Sacramento, throwing 14 pitches and striking out one.

Castro, acquired last year in the Troy Tulowitzki trade, has been good this year, but finds himself the odd man out among other hard-throwing right hander, Carlos Estevez. Together they are the only members of the Rockies bullpen with minor league options remaining.

Castro spent his own stretch on the disabled list due to shoulder inflammation from April 18 to May 18. When he was was activated from the DL in May, Castro was immediately optioned to Triple-A to rebuild his arm strength. He was recalled just a couple days later. After struggling at first, he has allowed just one hit in 2.1 innings pitched in three appearances in June. He will likely continue the rebuilding effort in this latest stint with the Isotopes.

The Rockies may be giving up one of their more reliable right-handed arms, but they’re gaining back the top left-handed arm out of the pen so far this season.