Alex Rodriguez is another interesting case. His walk rate is marginal, but his strikeouts aren't excessive for a power hitter. None of these guys has 30 walks and 130 strikeouts a year or anything like that. The defensive skills are range afield, fielding reliability, and throwing utility. Scouts usually consider fielding as a single category or tool, but I like to separate range and reliability.
Some guys have tremendous quickness and athleticism, and get to more balls than their counterparts.
But that doesn't mean they actually handle the ball reliably once they get to it. Conversely, some players are very sure-handed, but have limited mobility. Ideally, of course, you want both, but that is often a rare package, especially in minor league players. In the minors, the best defensive prospects are usually the guys with terrific range afield, even if they make a lot of errors when they are young. Reliability can be improved through hard work and repetition, but range itself tends to be organic.