Winter leagues can serve a variety of purposes. Sometimes players are sent there to get extra playing time due to injuries, sometimes players are sent there to be showcased, and sometimes players go on their own to places like Venezuela and the Dominican Republic to earn a little extra cash. While the small samples and inconsistent competition levels can produce dangerous assumptions, there are still plenty of players who have seen their stock rise during this offseason due to a combination of performance and scouting reports.
Jesus Aguilar, 1B, Indians
In a system desperate for prospects, Aguilar made some noise by slugging 23 home runs across Cleveland's two A-level clubs, but as a 240-plus pound bat-only player, scouts need to see him mash at the upper levels. That will have to wait until the regular season, but the 21-year-old has given evaluators two opportunities to see what is to come: He hit .339 with three home runs in 16 Arizona Fall League games, and followed that up with an equally impressive showing in his native country. If Aguilar can carry the momentum into the regular season, he'll be on more scouting radars.
Nolan Arenado, 3B, Rockies
Coming off a year in which he led the minor leagues with 122 RBI and batted .298/.349/.497 at High-A Modesto, it was going to be hard for Arenado to up his stock much. However, the 2009 second-round pick did so by earning Arizona Fall League MVP honors by hitting .388/.423/.636 in 29 games. However, it's not his bat that surprises scouts as much as his glove. He's improved his conditioning and worked hard on his defense, which has helped him transform from a player most thought would move to first to one who can stick at the hot corner. The Ian Stewart trade cleared Arenado’s path to Colorado, and he might reach the bigs by the end of the season.
Christian Bethancourt, C, Braves
Bethancourt is one of, if not the best, defensive catchers in the game. His arm is a pure 80; one scout reported a pop time of 1.68, the best he's ever recorded in his decade-plus of work. Offensively, the 20-year-old Panamanian has been a mixed bag; he has hit for a decent average but showed little in the way of power or patience. His approach still needs work, but after hitting five home runs in 72 Arizona Fall League at-bats, there's hope that his raw power might come around. The Braves hope he can show enough this spring to earn a Double-A assignment.
Robbie Grossman, OF, Pirates
Grossman had a breakout year in 2011, batting .294/.418/.451 for High-A Bradenton while leading the minor leagues in both runs (127) and walks (104). Those numbers also came in his second year in the Florida State League, and repeating a level is one of the biggest red flags among scouts. While the Arizona Fall League produces inflated numbers, Grossman's .375/.472/.625 line there left evaluators much more comfortable with his future. Continued success at Double-A in 2012 could land him in Pittsburgh in 2013.
Danny Hultzen, LHP, Mariners
The second overall pick in the 2011 draft did not help his stock as much as he accelerated his timetable. Hultzen was always seen as a quick mover, but he signed too late to make an official debut. However, he put up a 1.40 ERA in six starts while getting thrown to the wolves in the Arizona Fall League. Seattle just traded a potential star-level starter—Michael Pineda—and they feel Hultzen could be ready to audition for the role by September, if not earlier.
Bryan LaHair, 1B, Cubs
LaHair has gone from a Quad-A hitter to one scouts believe in. He was one of the best hitters in the minors in 2011 with a .331/.405/.664 line for Triple-A Iowa, and he was impressive enough in an end-of-season stint with the Cubs that he's been handed the first-base job, even after the acquisition of Anthony Rizzo. Though things are finally lining up for LaHair, he played in Venezuela this winter and dominated the league; he hit 15 home runs in 169 at-bats and drew nine intentional walks. Just as importantly, he spent some time in left field, hoping to prove that when Rizzo is ready, he'll be able to move, as opposed to just fade away.
Wil Myers, OF, Royals
Myers entered the 2011 season as one of the minors’ brightest young hitters, but nothing went right for him. He suffered a knee laceration early in the season, which later developed an infection. He was just never himself when he finished his season at Double-A Northwest Arkansas with an uninspiring .254/.353/.393 line. Scouts were willing to give him somewhat of a mulligan, but they were convinced it was a fluke when they saw the player they were looking for all year in the Arizona Fall League. With a big league-ready approach and electric bat speed, Myers hit .360/.481/.674 in 23 games, and while it was just six weeks, it left scouts believing he could reach the big leagues by September at the latest.
Mike Olt, 3B, Rangers
Olt was in the midst of a breakout season; he was batting .286/.395/.508 in a tough park at High-A Myrtle Beach when he broke his collarbone in a home-plate collision. Now, 54 games does not a breakout make, so after a rusty return to finish the regular season, Olt picked up where he left off by leading the Arizona Fall League with 13 home runs in just 106 at-bats while batting .349/.433/.764. He's also a plus defender at third base, but while his future is bright, Adrian Beltre is entrenched at the position in big leagues, so Olt’s future with Texas is a bit muddled.
Hector Sanchez, C, Giants
Sanchez was having a good year at High-A San Jose to begin the 2011 season, but everything changed with Buster Posey's season-ending knee injury. Sanchez was rushed through the system and even served a brief stint in the big leagues as the Giants scrambled for anyone who could play the position and hit. As good as he was in the California League, Sanchez’s Triple-A line was a lackluster .261/.315/.340. While he's scheduled to return there in 2012, he showed that he's more than just a California League mirage with a .339/.402/.548 line in 51 games for La Guaira in his native Venezuela; the power he showed in San Jose played in a much more difficult environment.
Tanner Scheppers, RHP, Rangers
Scheppers hasn't been the same pitcher since the Rangers briefly dabbled with making him a starter, but he showed signs of returning to his old self in Venezuela this winter. Scheppers’ classic two-pitch mix of a well above-average fastball and power breaker gives him late-innings potential. While he walked 13 in his 13 innings for Magallanes, he also limited batters to a 5-for-41 (.122) mark with 16 strikeouts. That's half of a major step forward for Scheppers, and the whiffs could land him in Texas in short order.
A version of this story originally appeared on ESPN Insider 
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So Sanchez is now a 22-year-old good-gloved catcher who hit for big power in A+ and the DWL, and showed a 8.8%B/17.6% BB/K approach in the big leagues. At 21. Why is this guy just sliding in at the end of Giants' top 10s?
He seems to have made strides in his defense as well, especially in terms of his receiving. Obviously, right now, almost anything would be a welcome (offensive) upgrade over the Stewart/Whiteside backup situation.