If you’ve just hit a thin shot, 9 times out of 10, your spine angle changed throughout your swing. What does this mean to the average player? It means that something forced your body to shift slightly upwards before impact. Usually this is caused by poor fundamentals such as standing too closely to the ball or having the ball too far forward in your stance. But without me seeing your swing, I can’t say for sure.
I have used this drill many times with my students to try and encourage them to maintain a more solid spine angle throughout each swing. It will work for you as well, regardless of your poor fundamentals (if you know your fundamentals problem, I recommend fixing that first before attempting this drill).
Through my studies of the golf swing, I have found that a good anchor for your spine is your eyes. By focusing your eyes on a specific spot during your swing, you can reduce the amount of spine movement you will have during your swing. I used the word ‘specific’ for a reason, using just the ball is not enough; choose a blade of grass or something smaller to focus on.
For this drill I used a tee; place a tee an inch or so behind the ball and address the tee, not the ball. Focus intently on the tee before starting your swing, and keep your eyes focused on the tee until after impact. You will be impressed with how effective this drill is at forcing you to make more solid contact with the ball. With some practice you should be able to maintain a more stable spine angle throughout your swing.
Give it a try!