The 20-year-old, who was taken down by snipers Saturday after wounding former President Trump, killing one person in the crowd and injuring 2 others ... tried to get in the rifle club, according to Frederick Mach, who currently heads the team and spoke with the NY Post.

Another member of the team when Crooks tried out, Jameson Myers, told the Post something was off with him ... something that just didn't sit right. He reportedly had odd interactions with the students and coaches.

As you know, Crooks was perched on a building just outside the perimeter of the Pennsylvania rally and began firing with an AR-15 style weapon. TMZ obtained video of Crooks as he began shooting ... 130 yards from Trump.

One former high school student says Crooks was bullied by other students and was described as an "outcast."

He was shot and killed within a minute of the time he began firing.