Toplines are always a point of contention for Borzoi and one of the most discussed points of the breed by both prospective and experienced judges. The standard reads, "Back: Rising at the loin in a graceful curve". Simple really, back is level, and the rise occurs at the loin in a graceful continuous curve to the pelvis. The standard does not say that the topline starts at the base of the neck nor does it say where the highest point should be. It is somewhat ambiguous and allows for some variation from a slight rise to a more pronounced rise, but there should be a rise. Standing the top line should never be flat or swayed. In motion it is flexible and can flatten out and even invert in the double suspension gallop at speed. If the back itself is not level it will impact the placement of the sternum in relation to the shoulder and the depth of chest at the elbow. The back and ribs are relatively short which also creates the underline due to the great depth of chest. This leads to a strong loin rather tucked up. An underline that is shallow in definition from chest to loin is wrong. If you have a short back and a topline rising at the loin this naturally will create a graceful curve. Neither too steep nor too slight are outside of the standard's definition of this breed element.
It is also important to note that too steep a fall away at the croup is also wrong. The hips and shoulders should be near equal in height. And the pelvis should not be too steep nor goose rumped. Balance here is important as it leads to an even gate with reach in front and drive off the rear. If the pelvis has too much of a steep angle from the loin the result is unbalanced movement lifting at the front and rear legs interfering. Sometimes the result is sidewinding down and back. Whether you see the movement that is incorrect first that leads to incorrect structure or feel an incorrectly proportioned inflexible topline the result will be the same unbalanced movement. Side gait doesn't have to have tremendous reach and drive to demonstrate the correct movement for a borzoi, but it does need to be balanced, effortless, smooth and grace. Note that both the definition of topline and movement uses the word grace or graceful. This is not by accident.
To sum it all up "short level back, topline rising at the loin in a graceful curve. Withers and hips near parallel, pelvis a smooth continuous line with the topline neither too steep or flat and a deep chest with a short rib cage well tucked up to the loin. Graceful in movement or repose, no abrupt angles, nothing that draws your eye away from a smooth transition from base of neck to tail". Considering topline is only nine words of the entire standard it can be the hardest thing to conceptualize by the fancy.