He and Kirke were both described as incompetent; this was particularly evident when Sloper knocked himself unconscious with his own bat. He expressed interest in continuing to play for Gryffindor, but was replaced the following year.
Sloper later delivers a message for Albus Dumbledore to Harry Potter with the details of their first lesson. He also asked Harry when tryouts would be held for Quidditch. Harry privately though that Sloper would be very lucky to gain a position on the team.
Jack derives from John, which means "God (Herbrew) is gracious".
Sloper could come from the English word slope,a surface in which one side is higher than the other. This could relate to his inability to do things right, since slopes have been described as very hard to climb for some people.