Grover was at a table on a football field with a few glasses of shakes when two bullies, "Bri-Dog" and Chet approached him, as seen in . "Bri-Dog" called Grover "Grove-error" and dumped some shake on his head. While leaving, Chet complimented "Bri-Dog" on coming up with that name and asked just how he came up with it. "Bri-Dog" told him he got the school's improv group the Lobster Street Players to give that to him by way of a threat. Suddenly, someone dressed in a ninja outfit filled a tennis ball machine with spit-balls and started it up, firing and bombarding the two with spit-balls. Grover witnessed most of what happened. Fillmore and Ingrid arrived on the field to ask questions pertaining to that. "Bri-Dog" decided not to go by that nickname anymore, preferring to be called by his real name, Brian, instead and he'd rather not talk about it. Since he was there too, Grover introduced himself to the two safety patrollers and said he saw everything except who fired the spit-balls. Then, Joseph found something suspicious that pointed toward Grover possibly being the one responsible.
In the Safety Patrol Headquarters' interrogation room, Grover confessed he thought about getting back at the bullies and wanted to, but he never really went through with it and he mentioned that his record was clean. But Fillmore and Ingrid showed him his permanent record file that proved otherwise, that he had served detention. Grover told them he got himself into detention purposefully, to escape the bullies, as he couldn't bear anymore torment. He also told them he had a fear of non-dairy whipped cream, which was what Wilbur happened to use.
After Fillmore, Ingrid, and Vallejo eventually figured out that Grover, Wilbur, Stella Valenzia, and Becca Baccadero spent time together in detention one Saturday when they decided to team up to take down the bullies, and that it was Stella who was the most likely suspect, Horace mentioned he had a computer system with a security camera that could pinpoint who was behind everything. Once the camera focused on Stella, Fillmore and Ingrid approached her, and off she ran. They went after her through the school's hallway, as the X Middle School Knitting Team were about to begin the quilting contest. Stella wound up entangled in a large yarn ball, rolling into the Converted Center Control Room, where the yarn ball loosened and she was freed. When Fillmore and Ingrid got there, they found that she, Becca, Wilbur, and Grover had taken Horace hostage, as requital for how he treated them. Just as Wilbur was about to damage to control panel by pouring gumbo onto it, Fillmore told them that there are other, better ways to solve problems with bullies. They said they were only trying to make a right, but Fillmore said they're just as much of bullies as well, that what they were doing wasn't the proper solution, and that they were better than that. They seemed to listen to and heed his advice. Everyone in the control room heard Principal Folsom announce the quilting contest winner as they watched a monitor. Grover and the three others served detention time once again, as revealed in the X Middle School Examiner.
Grover is voiced by Jack Johnson.