During the offseason, the Frontier League renewed their contract with the California Winter League.

This agreement between the CWL and the Frontier League has made the CWL the exclusive winter league of the Frontier.

To honor that agreement, the Frontier League has changed some of their eligibility rules for the 2018 season regarding pay to play leagues and any league that charges a fee to attend spring training.

From the official Frontier League website:

The California Winter League is the exclusive winter league of the Frontier League.

The Frontier League is proud to have extended our agreement with the California Winter League and to make the California Winter League the Exclusive Winter/Showcase League of the Frontier League.

Players who participate after May 1, 2018 in a pay-to-play league or a league that charges a fee to attend their spring training will be ineligible for the Frontier League unless the player has had contact with the Frontier League.

Contact with the Frontier League includes:
Having ever been under contract to a Frontier League team;
Having participated in a past Frontier League Tryout Camp and Draft;
Participating in the 2019 Frontier League Tryout Camp and Draft (for the 2019 Frontier League season)
Having participated in a past California Winter League season; or
Participating in the 2019 California Winter League season (for the 2019 Frontier League season)

Leagues that are covered by this provision are:
Arizona Winter League/Pro Prospect Winter Leagues, LLC
South Florida Winter League
Desert League
Pecos League
Empire League
Western League
Hudson Valley League
Thoroughbred League
Puerto Rican Instructional Baseball League
Urban League

Please note that this provision is not retroactive and only applies to players participating on one of these leagues after May 1, 2018.