You mean making the software proprietary. The definition of open source itself is neutral on whether it's a commercial effort or not, or whether it's a community effort or not, or whether it's both community and a commercial effort.
I think the main issue is the name. If a project is made more commercial or proprietary than it was before, please change the name (or additionally use a different name for the commercial/proprietary part, which seems to be common practice even when starting a project as partly open source). A clean break between different maintainers (particularly when a mostly single person effort) is a good reason to change the name too. Naming things is hard and it doesn't necessarily need to be all that different a name just something to reflect the change.
That's what "must be freely redistributable" means though.