Since his epiphany, he would frequently visit the children, but a clear storyline was still lacking until a boy named Ma Hu appeared and, like Xiaoshuang, quickly established himself as another point of focus for Xu's lens.

Ma from Ningxia Hui autonomous region appeared to be a typical example of the worst possible student a teacher can face: this angry boy frequently fought with teammates and was often disobedient, ignoring the guidance of the coach.

However, he needed to harness that strength and defiance in a more positive way if he was to achieve his goal of becoming a leader in the team.

"I was too naughty back then," Ma said with a giggle during a recent promotional event for the film in Beijing. "I'm not like that any more. My goal is to become a member of the national team in the future."

According to Xu's current plan, he will continuously record the group until they become adults.

"The diversity of their lives can be better displayed then," the director projects.

Currently, however, the sport is the shared goal of these "baseball angels".

Sun proudly says that the young players in the training camps are now among the best of their age group in China, and a strong collective honor is being established.

Last year, the children were even invited to play several games in a local teen tournament in the United States.

Sun confesses that he considered giving up the charity program at times, but he says there is no reason to quit.

"Once I gave up, the children would probably not only think I cheated them, but also that the world has cheated them," Sun says. "How can I do that?"

Sun recalls that people often ask him whether it is worthwhile to contribute so much to the project, and he says it is wrong to only consider himself as a "contributor".

"The spirit of the children gives us mental strength," he says. "To be fair, we also gain a lot."

Speaking about whether the popularity of Tough Out, which has made some of the children celebrities, will influence their healthy growth, Sun says: "I keep reminding them not to be cocky, but as future athletes, they need to get used to being in the spotlight－and when it shines on you, there is a responsibility to behave well.

"Whether the children will take baseball as their profession or not, they have already achieved so much," he continues. "By feeling the love of others, they will be able to go on and make a contribution to society in the future."

In November, Elemeet, a film distribution platform that facilitates a limited release of specialty films, and iQiyi, a major online streaming media platform in China, jointly launched a long-term project to create more screening opportunities for young filmmakers' arthouse movies and documentaries, which often lack the opportunity to be presented in mainstream cinemas in high quality.

Tough Out, which was also coproduced by Elemeet and iQiyi, is the first film to benefit from the project.

"The film offers more possibilities for storytelling angles in Chinese-language documentaries," Qi Kang, producer of Tough Out from iQiyi, says, explaining why the production was chosen to be developed into a feature-length film for cinema.

"We care about the lives of these youths," Qi says. "When humanities are mixed with business potential without too many restrictions on its format, really good content can reach a wider audience."