Do any of these statements sound familiar?

“In practice, I didn’t fumble once. Yet, during a game I fumbled a few times.”
“In practice, I hit 4 out 10 balls. Then during a game, I can only hit 2 of 10.”
“I easily make 8 out of 10 free throws at the end of practice, yet in games I’m shooting 40%. It doesn’t make sense.”
Do you find that at times you perform at a specific level in practice but are unable to perform at this same high level in the competition?
Certainly, numerous factors can come directly into play to impact performance and cause the differences between practice and competitive performance; components such as your opponent, environmental conditions, expectations of yourself and others, level of aggressiveness, confidence, strategies, tactics, and anxiousness all come into play.
That being said, let’s check out one factor that is going to influence your performance and, when addressed, can help you perform closer to your potential in the competitive environment, that is, the environment of your training.
As a dedicated athlete, you prepare to compete and win. You practice on a daily basis to enhance your athletic skills so that you can perform at your peak during a competition, whether it is to attain a personal performance or a team victory. Essentially, you train with the aim of performing at your best in the competitive arena.
The key question is - is your training environment actively structured to help you succeed in the environment of competition? With many athletes, this isn’t the case. Instead, practice is typically structured to help you perform well within a controlled training environment. Yet, players expect to be able to execute in competition at the same level that they practice at. It is like comparing grapes to oatmeal for the reason that the structure of practice and the competitive environment are completely different. This difference needs to be adjusted to improve overall competitive performance.
For many athletes, the specific practice environment is actually characterized by drills, repetitions, and putting the time in. Within this practice environment, you may not think about your internal dialogue, how you react to your mistakes, your attitude throughout the session as well as your confidence. The target is on the physical execution.
Additionally, many players do not practice the potentially adverse problems and situations that can arise in a competition, such as deafening crowd noise, faulty equipment or adverse weather conditions.
Compare your mental strength skills required in the training environment to those mental strength skills, the feelings, and behaviors that you’re required to demonstrate in the heat of battle. Top athletes desire (and need) to be self-confident. Top athletes want to maintain positive self-talk and be dedicated to what they need to do well. Top athletes need and expect to handle their emotions so that they don’t hurt their performance. Top athletes need to deal with expectations of their self and others, and need to manage their own reactions to the throngs of people or their challenger. This list could be almost endless and I think you're hearing the message right, so I won’t belabor the point anymore.  
So, how do you train and practice similar to competition? First, evaluate how you as a player require yourself to perform in competition, and then train those skills. For example: You want to maintain a positive attitude and focus on your overall performance. So, during training, work on managing your own self-talk and practice using inner dialogue and use words that will enhance performance.
If you want to work on your reactions to errors or frustration, then challenge yourself to do the same in practice. Work on the appropriate and empowering ways of managing your emotions.
Would you like to approach a competition with certainty, confidence, and a “must win” attitude? Then purposefully set your intention to do the same at practice.
To prepare with regard to external distractions, employ imagery in instruction to simulate the particular competitive environment. Based on your sport, it's also possible to prepare for the environment through bringing in “fans” to observe training, piping in noises or creating stress or challenging conditions.
Additionally, embrace problems when they present themselves. When you break a shoelace or your racquet string pops, rather than stop, continue to play through it. Use situations as much as possible and see them as opportunities to learn how to perform through adversity.
The end result is the more you can structure your practice environment to resemble your competitive environment, chances are your competitive results will improve. Your mental strength in practice will only help you reach your peak performance in competition.