As big media companies vie for pricey rights to pro sports broadcasts and streams, a smaller but equally hard-fought contest is breaking out for viewers of low-cost online videos about high school and college sports, esports and the like.The players in this contest are focusing on young, mobile-first audiences that are abandoning traditional TV, sports and viewing habits. The new players hope to leverage user-generated highlights, sports talk, social media, live-streamed content and more into a next-generation, ad-supported alternative to fading ESPN and even its subscription service ESPN+.The latest salvo: Two-year-old online site Overtime said today that it has raised $23 million in Series B funding from investors including the big VC Andreessen Horowitz, media company MSG Networks Inc. (tied to sports in New York's Madison Square Garden) and NBA stars Victor Oladipo, Carmelo Anthony and Baron Davis.Spark Capital led the funding round, with General Partner Bijan Sabet spearheading the deal. Boston-based Sabet has an admirable investing track record, buying in early on   sites such as Twitter, Tumblr, Trello. He also invested early on casual-game company OMGPop, which Overtime co-founder Dan Porter sold to Zynga for $180 million in 2012.Now, the investors are betting Overtime's mix of highlight videos, Fortnite esports, lifestyle programming and other content generated by a network of more than 1,000 paid stringers will help them become a next-gen ESPN for the next generation. It's beginning to pay off, as the company says its social-media followings have ballooned to more than 6 million, with more than 550 million views per month. The company is also creating original series for Snapchat and YouTube.Overtime and competitors such as Los Angeles-based Mars Reel are building their operations around mobile-friendly content about high school and college athletes and sports, targeted for YouTube, Snapchat and Instagram. The approach sidesteps the already brutal competition between traditional broadcast and cable networks that now are facing digital newcomers such as Amazon (and its Twitch unit), Twitter, and Facebook to provide live video of major professional sports games.Overtime recently expanded into women's basketball, and sponsors a pro e-sports team playing Fortnite, the hugely popular video game. The e-sports team's exploits also provide programming on Twitch and elsewhere. Separately, the company has begun creating programming in sports-adjacent lifestyle areas such as collectible sneakers and music."We founded Overtime to build the biggest sports network in the world,"  Porter wrote in a letter to users published today. "And we have made tremendous progress – thanks to our proprietary mobile camera capture technology, our grassroots efforts to literally be at thousands of gyms and fields worldwide, and thanks especially to our powerful community of athletes and fans."Porter's co-founder is Zack Weiner, a 26-year-old former chess champion. Overtime has now raised $35 million, from investors that also have included former NBA Commissioner David Stern, NBA star Kevin Durant, Sapphire Ventures through its Sapphire Sport investment platform; The a16z Cultural Leadership Fund, MACRO Ventures, Afore Capital and Correlation Ventures.Porter wrote that the company plans this year to expand into Europe, Asia and Africa, run more live events and marketing activations, extend its merchandising and e-commerce operations, and create more programming "to rival a traditional network.""The opportunity to build a new global sports network is massive," Porter wrote. "That’s why over the past year, we have expanded our focus to cover far more than just highlights. We have invested heavily in longer-form series, launching four on Snapchat and 13 on YouTube, many with 20-minute episodes and some now in their second and third seasons."