As Spring Training nears and we look ahead to the 2017 season, let's use Statcast™ data to answer one of the world's most pressing questions: Which collection of outfielders has the strongest throwing arms? Who will bring the most pure, raw velocity to the table? Given that you've likely seen the title of this article that states it's the Twins, we'll dispense with the suspense and admit that yes it's Minnesota.
That's true even without the rocket arm of Miguel Sano, whom we excluded, because he's likely to be strictly a third baseman or designated hitter in 2017, and we did the same for a few other players who were outfielders last year who are expected to play the infield this year, like Ian Desmond, Trea Turner and Jose Ramirez. The point here is to look at players who will be primarily outfielders this season and look at their "competitive throw" average over the past two years.
So yes, it's the Twins… but not by a lot over the Mariners. Just check out close they are. By our methodology, which we'll explain in a second, Minnesota's outfield arm average of 92.6 mph tops Seattle's 92.3 and Colorado's 92.2 by just a hair. 

So how did we measure that? And why the Twins?
First, this doesn't include every single throw, because as you might expect, not every outfield throw really "matters." Andrew McCutchen, for instance, had 354 tracked throws in 2016, but as you can see in the chart below, only a portion of them were thrown with intent. For example, on June 11, he fielded a Matthew Holliday grounder up the middle and tossed it back in to the infield at 48.1 mph. Does that tell you much about his arm? Not really. 

So the way we've identified "competitive throws" is to identify a player's 90th percentile arm strength, and then take the average of all throws above the 90th percentile, as a good proxy for tracking only throws where a fielder was trying to make play with some urgency. Of the 107 outfielders who had at least 10 such throws last year, Aaron Hicks' average of 99.4 mph was baseball's best (remember this?), and Khris Davis' average of 72.5 mph was the weakest. That's a big gap, yet it passes the eye test.
Since we're looking ahead to 2017, we've assigned players to their new teams if they've moved, so Adam Eaton is a National, William Fowler is a Cardinal, and so on. (We did not weight for expected playing time.) And since we now have two full years of Statcast™ data, what we've also done is to take a player's performance in both years, and give two-thirds weight to 2016 and one-third weight to '15. In most cases, that doesn't move the needle at all, but there are some players who saw arm strength increases (Stephen Piscotty jumped up due to mechanical changes) or decreases (Gregory Polanco lost 5.6 mph, possibly due to injury), so it matters.
Back to the Twins, what makes them so special? It's not that their overall average is pulled up by one standout arm so much as it is that every expected outfielder -- with one exception -- looks to be above average. Compare Byron Buxton (94.8 mph in 2016), Max Kepler (92.0), Danny Santana (96.8 mph) and Eddie Rosario (95.0 mph) to the Major League average on "competitive throws" of 88.9 mph, and they're all well above. The only outlier here is Robbie Grossman, who lags at a below-average 86.7 mph. But for a team that's notoriously had trouble finding pitching velocity, if you look at this crew and remember that they recently also had Hicks (who owns Statcast™'s all-time hardest throw of 105.5 mph) and Sano, it sure seems that outfield arms are a priority.

And what about the Mariners and Rockies? Seattle remade its outfield, keeping the strong-armed Leonys Martin (94.0 in 2016) but eliminating Seth Smith (84.5 mph) and Norichika Aoki (88.1 mph) in favor of Mitch Haniger (90.2) and Jarrod Dyson (92.0 mph). Colorado ranked fourth last year (91.3 mph), and it returns mostly the same players, though a full season of the strong-armedDavid Dahl (92.4 mph) ought to help further.
At the other end of the spectrum are the Giants and A's, neither of which is that surprising. If we show you the top five and bottom five of the 107 qualified outfielders from last year, you'll see each Bay Area team has a representative near the end.
Top five outfield arms on "competitive throws" in mph in 2016
99.4 -- Hicks, NYY
97.0 -- Starling Marte, PIT
96.8 -- Santana, MIN
95.8 -- Carlos Gomez, HOU / TEX
95.7 -- Jake Marisnick, HOU

Bottom five outfield arms on "competitive throws" in mph in 2016
72.1 -- Davis, OAK
77.7 -- Coco Crisp, OAK / CLE
79.5 -- Chris Young, BOS
79.7 -- Denard Span, SF
81.1 -- Delino DeShields, TEX
Now, it's true that we're measuring only pure strength, and not accuracy -- for now. But it's worth noting that we did this same exercise last offseason, and at the time, we projected that the Astros would have baseball's best cannons. Not only did that end up being very close to reality, as they ended up finishing second overall in outfield arm strength (92.0 mph), but their arms were effective. Houston led the sport in FanGraphs' "arm" metric, which is defined as "the amount of runs above average an outfielder saves with their arm by preventing runners from advancing," and actually put up one of the five best seasons on record, dating back to 2002.
We did note, though, that the Astros finished second in overall arm strength last year. Who was No. 1? It was the Twins, at 93.3 mph. A rebuilding Minnesota team may not be ready to compete just yet, and it may not approach .500. It doesn't mean there's nothing fun to watch at Target Field, however. Keep your eyes trained on those outfield rockets.