Raglan sleeve

A raglan sleeve is a sleeve that extends in one piece fully to the collar, leaving a diagonal seam from underarm to collarbone.
It is named after Lord Raglan, the 1st Baron Raglan, who is said to have worn a coat with this style of sleeve after the loss of his arm in the Battle of Waterloo. The Raglan sleeve was invented by coat producer Aquascutum for Lord Raglan to allow him room to use his sword in battle. It gave greater movement to the wearer, instead of the usual sleeve head which was prefixed.
The raglan mid-length sleeve is a popular undergarment (worn under the jersey) for baseball teams in MLB.