In some areas of the country, qualified teachers are harder and harder to come by for certain content areas. Some states and districts have had to use creative means to find teachers. One of these avenues is using transition to teaching programs in order to find teachers. In these programs, individuals usually have a degree in a content area, such as science or math, but lack the credentials or experience necessary for teaching.
As with most things, there is an upside to these teachers as well as some drawbacks. It does allow your school to think outside the box to fill positions, which is a major advantage. At the same time, it is good to consider what the possible potholes will be of hiring one of these teachers.