A player who can be projected to be nothing more than adequate defensively can be drafted if he can hit and hit with power. He doesn’t need to have a good arm, or run fast.
Truth is that if he is one of the best at hitting and hitting with power, he is most likely to be drafted very early. It’s not so often that the best hitters (even without another plus tool) go later in the draft. The best hitters get picked early.
So, there has to be something else besides the bat (defense) that is at least playable. But the bat alone can be worth millions in that case.
Example of a couple first round picks…. Prince Fielder and Billy Butler! If they would have graded out below average as hitters… Their other tools would not have gotten them drafted. Both are good Major League hitters and that is the only reason why they are there. They are not there for any other reason, even though Prince is not a slow runner and Butler has a nice arm! When you see a player getting drafted and his draft position is listed as left field or first base… He got drafted because of his bat… anything else is just a bonus, for the most part.