Ragnar Sandberg grew up in Stenungsund in Bohuslän. He long chose between becoming a writer or a painter but eventually sought admission to Valand School of Fine Arts, where he studied under Tor Bjurström from 1920 to 1925. He then devoted himself to writing for a few years. In 1929, he began painting again, stimulated by Ivan Ivarson, and ten years later, he had his breakthrough as an artist with solo exhibitions at, among others, the Svensk-Franska Konstgalleriet in Stockholm. However, he continued to write and is considered the sharpest theorist among the Gothenburg Colourists.

From the mid-1930s, Ragnar Sandberg developed his interest in movement and rhythm. In 1936-37, he travelled to France, where he became acquainted with Bonnard's poetic painting, his sensual colours, and time-consuming glazes. On the same trip, Sandberg saw paintings by the Spaniard Francisco Borès, whose darkness influenced Sandberg.

Full of new impressions, he returned to Gothenburg and allowed his canvases to be filled with Gothenburg motifs, still lifes, and bathing West Coast residents with strong colour. He engaged in endless variations and repetitions of everyday motifs such as cyclists, croquet, and football players in motion.

Characteristic of Sandberg's painting during this period are bright, lyrical pastel colours in the main subject, often contrasted with a stringent, dramatic darkness in the details. He constructs his images like puzzles, where different parts overlap each other, and he enjoys creating patterns of light and dark. The common denominator is, like for several of the Gothenburg Colourists, a dissolution of form and an expressive handling of colour. Sandberg was a profound artist and worked very methodically with his compositions, sometimes with almost mathematical precision.

The painting "Krocketspelarna" (The croquet players), was executed during this period and appears in an earthy palette. Three children are lined up in parallel, completely absorbed in the ongoing game.