I have copied below excerpts from an excellent article written by sailing legend and coach Dave Dellenbaugh of https://www.speedandsmarts.com regarding losing sailing control on the race course. In the article he speaks about what happens when you lose control of your strategy, tactics and race.
Techniques to avoid being controlled
You must work hard to avoid being pinned by your competitor, and you should know how to escape when you’re taken down.
At the same time, you have to go on the offensive. A classic example in sailing is the pre-start circling that happens in match racing. Here each boat circles to get on the tail of the other boat (offensive) and to keep the other boat off their tail (defensive).
To avoid being controlled on the race course the most important thing is anticipation. Keep thinking ahead and avoid situations where you could get trapped.
Stay away from the corners and laylines.
The closer you are to the sides of the course, the easier it is for someone to control you. So try to stay closer to the middle, where you keep the option to go either way.
Find lanes of clear air.
Clear air is key in following your strategy. So keep looking up the course for channels of undisturbed wind that will let you sail in the direction you want.
Avoid overlaps with other boats.
It’s usually dangerous to sail upwind or downwind very near other boats. The closer you are to your competitors, the more likely it is they’ll interfere with your plans.
Communicate your rights.
Loud hails are recommended not only for safety reasons, they’re a good way to keep other boats from infringing on your space. A typical example is yelling “Hold your course” when you duck a starboard tacker.
Techniques for controlling other boats
Use your wind shadow.
The large area of disturbed air to leeward of your sail plan is your most effective tool for affecting other boats.
Pinning and blocking.
Often the best way to “herd” another boat is simply to use your physical presence. For example, you can prevent another boat from tacking by setting up just to windward of them on the same tack.
Steering a converging course.
Your right-of-way under the rules is another tactical tool for helping you gain control. The best example I know of is when you’re on starboard tack and you bear off at a port tacker to prevent her from lee-bowing you or squeezing around the windward mark ahead of you.
How to improve your tactical skills
Learn the racing rules.
Knowing the right-of-way rules is an incredible confidence-builder when you get into tight situations.
Try match racing.
This one-on-one competition offers the ultimate experience in tactical control. The more you match race, the more comfortable you’ll feel whenever you’re near another boat on the race course.
Sail in tight, close, competitive fleets.
You have to get your feet wet if you really want to become a better “tactician.” Fleets of small one-designs are perfect for this.
If you want to come out on top, you can’t be passive. It’s nice to be laid-back at times, but if you want to avoid being stepped on, you have to assert your rights.