Initially, when Carlos Santana came to the Indians and said he wanted to play third base this year, they were willing to wait back and see what he could do in the Dominican Winter League. Now, they have taken a more proactive position. During practices, Santana has been exclusively taking ground balls at third (alternating with Lonnie Chisenhall) and has started four of the nine Spring games so far at the hot corner (Chisenhall started the other five).
One thing that hasn't happened is Santana playing any innings at catcher or first base. This is most likely because the Indians believe he has those positions down, despite having a below average glove and range at first in previous seasons. His versatility this season will largely depend on his ability not only to play third, but also to catch and play first. The positives if he is able to do this are obvious. He could save the Indians as many as two roster spots by being able to be the starting DH, back-up catcher and back-up corner infielder. This would allow the Indians to carry an extra outfielder for more speed on the bases or stronger defense and an extra reliever in the bullpen. For this to happen, however, his defense at third needs to be passable or he will just hurt the team more than the added value of the other players.
During practice, Santana completed a far larger percentage of plays than Chisenhall, but this is so far removed from actual game play that it is not a very good analyzer. The problem with actual game play is that it is random. The chances of any ball going to third are pretty rare in baseball and it is even rarer to have the type of plays that are difficult but still make-able. Santana has proven this to this point, only fielding four balls, one of which he made an error on. Small sample sizes like this are virtually meaningless and even if he played every other game at third for the rest of the month, it could be hard to get a real understanding of what level of defensive third baseman he will be.
There is another part of this equation however, and Santana is made to look better by competing against one of the poorer defensive third baseman in the league. Despite his best fielding percent in his career, Chisenhall's .955 in 2013 still fell within the bottom third of all qualifiers at third. Because of this, Santana could be the worst defensive third baseman in baseball and still be able to make up the difference in his bat.
Even if Santana proves that he can play third base at a Major League level, he won't likely be the starting third baseman. In a best case scenario, he would likely play third against left handed pitchers, allowing a right handed batter to replace Chisenhall in the lineup. Because of this two or three times a week schedule, it will matter even less that Santana can't turn himself into a Gold Glover overnight. The next question will be whether or not he allows the defensive transition to affect his abilities at the plate. This happened to the last player the Indians tried to switch to third base, Jhonny Peralta, and it will be unknown how it will affect Santana until well into May.
This certainly looks like a man who is comfortable at the hot corner.