Contreras was a rather obscure prospect entering 2015. A Venezuelan signed in 2008, he was a .260ish hitter with mediocre strike zone judgment and promising but inconsistent defense. That changed last year when he improved his eye at the plate and put up a .333/.413/.478 line for Double-A Tennessee.
He received a huge amount of hype over the winter from Cubs-oriented sources, hype that I thought was a bit excessive.
From the 2016 Baseball Prospect Book:
Willson Contreras, C, Chicago Cubs
Bats: R Throws: R HT: 6-1 WT: 175 DOB: May 13, 1992
I will preface this by saying that I like Willson Contreras. I like his improved plate discipline, his wiring strength, his athleticism, and his defensive tools. He certainly had a fine year in 2015, leading the Double-A Southern League in batting average. That said, he is getting a lot of hype this winter in Cubs circles and it strikes me as somewhat excessive if you look at the whole package. 2015 was the best season of his career by far, out of context actually. Real improvement, or a fluke? Probably some of both. At age 23 (24 in May), he doesn’t stand out especially for youth. He still has work to do with the glove. He looks good back there tools-wise, but threw out less than 30% of runners and is still prone to mental lapses. He’s a fine prospect but non-Cubs-oriented sources are not necessarily gushing in love with him yet. I want to see how much of this progress he maintains before going higher than a Grade B-.
And what do we think now?
Contreras has remained hot, hitting .350/.439/.531 for Triple-A Iowa. Yes, that's the Pacific Coast League, but even adjusting for context it is a terrific season, even better than last year, his wRC+ increasing from 156 (already excellent) to 176. Both his walk rate and isolated power numbers continue to improve, without any serious increase in strikeouts. This fits scouting reports from Iowa sources that Contreras is truly locked in, maintaining the improved approach he developed last year, handling both fastballs and breaking stuff well and showing power to all fields.
What about defense? Well, that's gotten better, too. He's always shown strong pop times but his actual ability to cut down runners was less than stellar. That's improved a bit this year, with 31% of runners caught, not excellent but playable. His other defensive skills have sharpened up; a former third baseman, he's steadily lowered his error rates. He'll still make some occasional receiving miscues, but all the tools are there and the skills have improved.
At age 24, Contreras has nothing left to prove in the minors as a hitter and his glove is not far behind. Triple-A is no challenge for him at this point; he is ready to move up.
Bottom line: people who were enthusiastic over the winter were correct and my report from the book was too skeptical. I'd rate Contreras as a Grade B+ at this point and one of the top catching prospects in baseball.