Baseball fans were all over Ted Cruz during Sunday night's playoff game at Yankee Stadium ... booing the senator relentlessly and flipping him off as he moved around his seat behind homeplate.
The Texas politician -- a huge Astros fan -- showed up to the Bronx wearing orange and blue to cheer on his favorite team as it tried to punch its ticket to the World Series with a win over the Yankees.
Cruz was seen smiling before the opening pitch ... but throughout the night, he was NOT received well by fans near him.