My post above with the NCAA rule in it seems to state that in any sport, as soon as a player sets foot on the court in a regular season, the chance of redshirting is gone.
You are correct. If you play one minute, you cannot take a voluntary, non-injury related redshirt.
The confusion probably stems from the medical redshirt rule. If you play, and get injured, you can receive a medical redshirt as long as you have played in less that 30% of the total regular season games. This was changed four years ago, it used to be 20% of total games.
If a player were to be injured, there is some gray area space around what constitutes a serious enough injury to justify a medical hardship. For example, if Clayton were to sprain his ankle, then not play again for the year, he probably would be able to qualify for a medical redshirt. There isn't a lot of scrutiny surrounding the first medical redshirt, providing that it meets the 30% rule. A second medical redshirt will have a lot of scrutiny, and is not often allowed.