FastballAPI
MLB since 2015 plus college baseball: pitches, plate appearances, box scores and sportsbook odds

Fitbit Information.
Fitbit API is a free Sports & Fitness API that requires OAuth authentication, is served over HTTPS and has unconfirmed CORS support.
You'll fit in here. Using JavaScript, CSS, and SVG, developers now have a fast, easy way to build apps and clock faces for Fitbit OS.
Details from dev.fitbit.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
MLB since 2015 plus college baseball: pitches, plate appearances, box scores and sportsbook odds
Real-time FanDuel Sportsbook odds — live & in-play and pre-match, with a keyless public snapshot
Embed codes for goals and highlights from Premier League, Bundesliga, Serie A and many more
F1 data from the beginning of the world championships in 1950
Tables, results, model probabilities and Monte Carlo season projections for 93 leagues
The Fitbit API is provided by Fitbit SDK (dev.fitbit.com). You'll fit in here. Using JavaScript, CSS, and SVG, developers now have a fast, easy way to build apps and clock faces for Fitbit OS.
Yes. The Fitbit API is listed in the Sports & Fitness category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Fitbit API uses OAuth authentication, so you need to register for credentials before making requests.
CORS support for the Fitbit API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Fitbit API is served over HTTPS, so it's safe to use in production.