Cobbold starred on his international debut in England's 7–0 demolition of Ireland in February 1883, scoring twice in three minutes, and was frequently described as the trickiest and most elegant forward in the world at this time. "If one were to ask, Who were the three greatest forwards of all time?" wrote William Pickford and Alfred Gibson in 1906, "no matter what other two were named, W.N. Cobbold would perhaps come first to the lips."

Playing generally at inside left, "Nuts" was considered to have the ideal build for a striker of his period. "The best type of forward player," wrote Montague Shearman in 1887, "is the fast, sturdy man of medium height, like W.N. Cobbold the Cantab." It was true, Pickford and Gibson went on, that Cobbold was pre-eminently an old-style dribbling forward, who had learned his football in the years before the advent of the "combination" (passing) game at the end of the 1870s: "In those days 'dribbling' was the great game, and one only passed the ball when one was completely hemmed in, and not always even then." But "Nuts" was far more than a mere dribbler, the authors stressed:

"He was essentially a scoring forward, and one, too, that made most of his own chances. One could not, for instance, conceive a greater contrast in style than Cobbold and Bloomer, both inside forwards. The former was almost continuously on the ball, while the Derby man seems to be doing nothing, and doing it well, for the greater part of the game. When Cobbold got possession of the ball he seemed to keep it glued to his toe, darting hither and thither as he pursued a tortuous course towards goal. One man was practically powerless to stop him. Two men might stay his career by dividing their attentions between the man and the ball, but they were not always successful even then. Very frequently Cobbold would shoulder his way through a whole crowd of the opposition and emerge triumphant with the ball at his toe. He was built for hard, strenuous play."
G.O. Smith, the great centre forward who followed Cobbold to Charterhouse and into the England team, concurred with Pickford and Gibson, recalling "Nuts" in April 1943 with the comment: "I put him first among all the forwards I have known." Smith's verdict – coming from a noted student of the game and a man who had played with and against strikers of the calibre of Steve Bloomer and Billy Meredith – may be considered to restore the now almost entirely forgotten Cobbold firmly to the foremost ranks of footballers of all periods.

Cobbold's other great attribute was his speed. In his prime he was a considerable sprinter, his obituary in The Times recalling: "Who that ever saw him speeding away down Parker's Piece will ever forget it? He was extraordinarily hard to stop and extremely fast." Although in essence a one-paced player, lacking the ability – so conspicuously displayed by Stanley Matthews – to stop, start and accelerate, Cobbold nonetheless possessed the exceptional ball control required to make him a most daunting opponent. "No man that ever played," wrote Pickford and Gibson, "could control the ball so effectively as Cobbold could when travelling at full speed... [He was] inimitable, the finest and fastest dribbler the Association game has known."

To his abilities as a runner and a dribbler, moreover, must be added great prowess as a goalscorer. Cobbold was renowned for his marksmanship, and it was commented that, given two feet of goal to aim at, "Nuts" would invariably hit the target. The striker had, most contemporaries agreed, one of the fiercest shots yet seen. "He could shoot in any position," was the verdict of Pickford and Gibson, "and he sent the ball in like a charge from a hundred-ton gun."

Cobbold anticipated the professional game in one respect (noted Edward Grayson, the historian of the early amateurs), "for in order to avoid getting hurt, he turned out swathed in rubber bandages and ankle guards." He belonged, nonetheless, resolutely to the earliest period of Association Football, disdaining – in common with many footballers of his generation – the aerial game, then regarded as a novel and distasteful innovation, and "eliminating all heading from his play." "Nuts" also declined to modify his dribbling style with the advent of new tactics for "passing forward" in the early 1880s – partly, speculated Pickford and Gibson, "because in his day they had not been sufficiently developed and partly because he himself was a man of infinite resource." Those who had seen the player in his prime sometimes debated how "Nuts" would have fared against the better organised defences of the 1890s. "The chances," Gibson and Pickford concluded in their assessment, "are that against three of our strongest half-backs he would have had to considerably modify his methods."

Cobbold accumulated a total of nine England caps, a good number at a time when only three international matches were played each year, scoring six England goals in total. His final international appearance came in a narrow March 1887 defeat to Scotland.