This is a vintage 1960's Champion Running Man cropped football practice chimel shirt, it is in excellent condition and labeled as a size 44 but fits best as an adult medium. Measurements below:
pit to pit: 19"
length: 16"
More on this shirt can be found in the Tags & Threads Guide to Champion book, here is some info on this shirt from the book here: "The half-length version of style 77QS, known as the "shimmel" shirt, was originally designed to be worn underneath football pads. These heavyweight T-shirts prevented chafing from pads while also allowing more air circulation compared to the full length 77QS. Shimmel shirts were issued mostly to football teams as part of their practice uniform. In 1971 or 1972 it crossed over to the bookstore market becoming a popular casual style for women. In the 1980s, it was heavily promoted to men in the retail market as a new activewear fashion."