I would offer a suggestion and two points of perspective on this topic.

The suggestion: this is a terrific conversation, but probably should be occurring in the "Other" section of the forum.

First Perspective: You might be over analyzing the term red shirt as it applies to athletics. I trust that you have researched the topic and the term red shirt would apply those individuals involved in political actions against republicans.

I hope to research it later, but it might be possible that the term is actually much more innocent than your conclusion. It may be possible that the first team to use or request an extra year of eligibility for athletes not yet suited for college ball, outfitted their ineligible athletes in red practice jerseys so that they could be easily identified on the field. It would be similiar to placing the Red Jersey on the QB indicating "stop, don't hit me during practice." (I just did a quick search and the one of the first known athletes to extend his eligibility was from the University of Nebraska and this might have a better correlation to the term "red shirt")

Second:
School district finance is based on property tax revenue. Lower socio-economic regions of a community generally generate less revenue from residential property tax, but receive higher revenues from the commercial/industrial properties in the area. The mitigating factor is that all revenue from local property tax is then placed in the public school system budgeting process. It is not disaggregated based on its source (ie. this money came from the NE side of town, so it has to go to the NE schools), it is distributed based on budgetary concerns and needs of the entire district.

A more recent infusion of the term red shirting, is now being used to apply to kindergarten children lacking the skills for kindergarten readiness based on the age and gender of the child. It is being used mostly for boys which mature later than girls. Five year old girls statistically demonstrate ready-ness, whereas young five year old boys are demonstrating a need to have an additional year of maturity to close the achievement gap. Thus the phrase "kindergarten red shirt" is gaining momentum. I have a feeling this is more of a link to the college use of the phrase, as opposed to a segregtory phrase from the 1700's. As with any educational issue, socio-economic issues also contribute to kindergarten-readiness, which invariablly switches to a conversation on race and culture.

Finally, what might be more interesting, is to look at the Republican (Blue States) and Democrats (Red States) connection with your political assertions. Is there a connection between the red state - red shirt?