During the scene, right after the first playground skirmish between the Jets and Sharks, which gets broken up by Lt. Schrank and Ofcr. Krupke, when Bernardo and the Sharks had been banished from the playground by Schrank and Krupke, and they were walking near the wall, after Bernardo had pounded the wall with one fist in his anger and frustration, he and the Sharks seemed to have an expression of sadness along with the anger at the racism that they experienced at the hands of the Jets, who didn't want the Sharks vying for their territory. Yet, at the same time, Bernardo and the Sharks as a whole, seemed determined to fight for their share of the small piece of turf that had been allocated to both the Sharks and the Jets by our society, and our system, as a whole. When Bernardo and Riff went down for the final count after the Rumble, there was an expression of sadness and anger on the part of the rest of the Jets, and Baby-John, the youngest Jets member, had been moved to tears.
The Jets, although tough as well, wore facial expressions that seemed to combine toughness, cockiness, arrogance, anger, and a touch of sadness along with all the other emotions and behaviors. By the facial expressions that the Jets wore, it was fairly easy to tell that their emotions, as well as those of the Sharks, were quite mixed. Two groups of have-nots were put in competition with each other for what little turf had been allocated to them, which ultimately resulted in racial, ethnic and cultural hatred, constant conflict with the law, competition with each other at the dance at the gym, and the ultimate show-down (i. e. the Rumble) between the Jets and Sharks that resulted in three deaths; Riff, Bernardo, and Tony.
Bernardo's girlfriend, Anita, who was also Maria's best friend and confidante, clearly disapproved of Maria and Tony's relationship, and her facial expressions, which were a mixture of disbelief and hostility, also indicated that. So was Anita's initial reluctance to go to Doc's Candy Store to warn Tony about Chino. The faces of the Jets, however, turn into total anger and sadness when Anita went to Doc's Candy Store in order to warn Tony about the fact that Chino was gunning for him, but the Jets, due to hatred and fear of Anita due to her ethnicity and culture, as well as being afraid that Anita would tell Chino that Tony was hiding out in the basement of Doc's Candy Store, not only refused to listen to her when she tried to convey the message to the Jets about Tony, but began to insult Anita and physically rough her up. The Jets, constantly angry, wore facial expressions that depicted the lack of conscience about what they'd done to Anita, until they were pulled up s
hort by the arrival of Doc himself, whose facial expression, always one of frustration and resignation, now turned to one of complete anger when he saw the way the Jets had treated Anita.
Lt. Schrank's facial expressions were noticeably of frustration and anger, after years of experience in dealing with gangs and their criminal exploits and behavior, and Ofcr Krupke's expressions of anger, frustration and resignation, were there, although somewhat more subtle than those of Lt. Schrank.
During the War Council between the Jets and Sharks, the Jets, including Riff and Ice, were clearly angry, and the Sharks, who were quieter, were both angry and sad. Yet, at the same time, the Jets had their moments of fair play; accepting Bernardo's suggestions of when and where the Rumble would be held, and refusing to disclose the whereabouts of the Rumble to Lt. Schrank when he asked them, and offered to "lend the Jets a hand if things got rough".
Both the Jets and Sharks no longer had expressions of anger after the Rumble with its three deaths, but expressions of sadness, as well. When Riff was knifed by Bernardo, the Jets' anger had clearly dissipated, with expressions of sadness that seemed to almost overwhelm what ever anger they'd felt, but not quite, if one gets the drift. The same can be said, I think, when the Jets, the Sharks and their girls were lined up, though still initially taking sides, all came out on the playground together after Tony had been gunned down by Chino, in retaliation for Tony's having knifed Bernardo to death during the Rumble, and in jealousy because Maria had come to love Tony rather them him (meaning Chino).
Maria, who'd always been more optimistic and believed that love conquered all, because less optimistic, though she still loved Tony, despite his having killed her brother. Her anger at the Rumble with the Jets' and Sharks' hatred of each other made Maria quite angry, which one could see, by her facial expressions, which immediately turned to sadness after Tony's death.
When people are in constant conflict with each other, it has an affect on their facial expressions, and the Jets and Sharks in West Side Story were certainly no exception.