It basically means that he's got a lot of tools, but hasn't developed them to the point where scouts feel they can safely say what he will end up as.
In Nurse's case, it means he's thrived by simply using his physical abilities, rather than hockey techniques.
- Jsaquella
i interpret that phrase to mean the prospect needs A LOT of development, which i then interpret to be an exaggeration because of his likely high draft position. i see it used enough that for me it waters down the criticism and seems like a vague catch-all phrase that loses its value when describing someone's potential.