High school football teams frequently participate in controlled scrimmages with other teams during preseason practice, but exhibition games are rare because of league rules and concerns about finances, travel and player injuries, along with enrollments not being registered until the early part of August in most school districts under the traditional September–June academic term. A more common exhibition is the high school football all-star game, which brings together top players from a region. These games are typically played by graduating seniors during the summer or at the end of the season. Many of these games, which include the U.S. Army All-American Bowl and Under Armour All-America Game, are used as showcases for players to be seen by colleges.
Who frequently participate in controlled scrimmages?