Teacher cognition (Borg, 2015) of grammar instruction is a relatively new phenomenon that has yet to be explored in the Saudi context. While many studies have focused on the teaching of grammar in general (Ellis, 2006; Corzo, 2013; Braine, 2014), further research needs to be done - particularly when it comes to understanding teachers' beliefs of grammar and grammar instruction as well as their practices in the classroom. This case study investigates the relationship between teachers' beliefs of grammar and grammar instruction and their instructional practices. In the first stage, a sample of 30 teaching faculty members at the English Language Institute (ELI) at the University of Jeddah (UJ), in Saudi Arabia completed a survey discussing their beliefs related to grammar instruction. In the second stage, ten of these teachers were observed in classroom in order to explore the relationship between their beliefs and practices. In the third and final stage, open-ended questions were distributed to the teachers after the observations to better understand the factors that influence their beliefs. The findings reveal that teachers' beliefs are indeed reflected in their classroom practices. Students' proficiency level, attitudes toward the language, needs, learning styles, classroom environment, and teacher development are six factors that influence the transformation of teachers' beliefs regarding grammar and grammar instruction into practices. These findings will help broaden the discussion on how to improve the quality of grammar teaching, particularly in the Saudi EFL classroom.