Trade rumors seem to swirl around Rays right-hander Chris Archer on a regular basis, and it's not difficult to understand why pitching-hungry clubs would have keen interest.
Archer is a 29-year-old two-time All-Star with a history of good health, nasty stuff, an engaging personality and a team-friendly contract. And in a sport in which workhorses are becoming increasingly rare, he is one of just four pitchers to throw at least 190 innings in each of the past four seasons, along with Corey Kluber, Max Scherzer and Jeff Samardzija.
At the same time, Archer remains a bit of an enigma.
By some measures, a club could view Archer as one of the best starters in the game. By others, he appears less exceptional.
If this is the year when a team finally takes the plunge and swings a long-rumored trade for Archer, exactly what would it be acquiring? Here are four ways in which the Tampa Bay righty is unusually difficult to evaluate.

1. Recent results
After a brief debut the year before, Archer stepped into the Rays' rotation in June 2013, and during the next three seasons, he posted a stellar 117 ERA+, reaching at least 112 each year in the park- and league-adjusted stat (100 equals league average). Of the 89 pitchers who threw at least 400 innings from 2013-15, Archer ranked 21st in ERA+, and he did so at ages 24-26.
Yet, Archer has limited runs at an almost exactly average rate since then, with an ERA+ of 100 in 2016 and 101 in '17. Overall, he ranked 57th of 92 pitchers during that time (minimum 250 innings). That's certainly not bad, but it's also not a positive trend.
In contrast, from 2013-15, Stephen Strasburg threw almost the same number of innings as Archer, at the same ages, with a 120 ERA+ that was just slightly higher. But in the two years since, Strasburg has taken a step forward with a 144 ERA+, and in '17, he finished third in the race for the National League Cy Young Award.
Of course, ERA is far from the only way to view a pitcher. Going by the Statcast™ metric of expected weighted on-base average (xwOBA) -- which considers a pitcher's quality of contact allowed, plus strikeouts and walks -- Archer was nearly as good in 2017 (.288 xwOBA) as in '15 (.281). However, Archer's actual wOBA allowed was 37 points higher last year (.311), suggesting that external factors might have played a big role in any underperformance.
2. Do the splits
During those past two seasons, Archer has been two completely different pitchers at Tropicana Field, versus on the road.
From 2016-17, there were 110 pitchers who made at least 20 home starts, and also 110 who made at least 20 road starts. Among those, Archer ranked 15th in home ERA (2.96) but 89th in road ERA (5.21). And it isn't just about that one stat.
Archer's 2016-17 splits
FIP: 2.82 (home), 4.43 (road)
K percentage: 31.2 percent (home), 25.5 percent (road)
HR/9: 0.9 (home), 1.7 (road)
OBP allowed: .283 (home), .320 (road)
SLG allowed: .346 (home), .464 (road)
Perhaps this is just a two-season blip. After all, Archer actually was slightly better when he pitched on the road from 2012-15, with a 3.27 ERA that ranked 12th in the Majors (minimum 40 starts). Still, the recent splits are a complicating factor.

3. Whiffs, and what else?
One puzzling aspect of Archer's past two seasons is that his ability to limit runs has not kept pace with his elite ability to pile up strikeouts.
Since 2016, there have been 159 pitcher seasons of at least 150 innings. Archer's strikeout rates (27.4 percent in '16, 29.2 percent in '17) both rank in the top 20 among that group, but his ERA+ numbers tied for 92nd and 98th.
Another way to look at it is that during the past 10 seasons, pitchers who have finished in the top 10 in the Majors in strikeout rate in a given year (minimum 150 innings) have averaged a 137 ERA+. Just 16 of the 100 posted an ERA+ below 110, and Archer's 2016 and '17 campaigns both were among the eight lowest in terms of ERA+.
Part of the problem is that while home runs have shot up across baseball in the past couple of seasons, the trend has hit Archer particularly hard. Among pitchers with at least 250 innings during the given two-year span, Archer ranked 17th in HR/9 from 2014-15 (0.69) but 61st from '16-'17 (1.28), as his rate nearly doubled.
4. True value
Different forms of Wins Above Replacement (WAR) calculate a pitcher's value in different ways but often come to similar conclusions. For example, the top six in total FanGraphs WAR (fWAR) and Baseball-Reference WAR (bWAR) during the past two seasons are the same pitchers, just in slightly different orders.
Archer's performance, on the other hand, has created a huge divide.
fWAR uses FIP -- which is based on strikeouts, walks and home runs -- and puts Archer 11th in MLB during the past two seasons, at 7.7. But bWAR uses actual runs allowed and puts Archer 71st (minimum 200 innings), at 2.9. By the first measure, Archer ranked just ahead of Jacob deGrom, but by the second, he slotted in just behind teammate Jake Odorizzi.
From 2016-17, 129 pitchers threw at least 200 total innings. None had a wider gap -- positive or negative -- between those two WAR figures than Archer (4.8). Only one (Ian Kennedy) matched the 60-spot gap between Archer's rank in those categories.
That speaks to the difficulty of evaluating Archer, an in-demand pitcher with both obvious appeal and some obvious question marks.